F. Ren - Academia.edu (original) (raw)

Papers by F. Ren

Research paper thumbnail of Conduction mechanisms in W and WSix ohmic contacts to InGaN and InN

Solid-State Electronics, 1997

The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0... more The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0.65Ga0.35N and InN was measured in the range −50–125°C. The results were compared to theoretical values for different conduction mechanisms, to further elucidate the conduction mechanism in these contact structures. The data indicates the conduction mechanism is field emission for these contact schemes for all

Research paper thumbnail of (Invited) Fundamental Modeling of Radiation Effects in AlGaN/GaN HEMTs

ECS Transactions, 2014

ABSTRACT AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They ... more ABSTRACT AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They are also well suited for high power and high frequency applications and thus may be advantageous for satellite-based communication systems. Radiation studies have shown the following DC performance changes: threshold voltage shift (positive), transconductance reduction, and saturation drain current reduction. The basic phenomenon leading to degradation of DC performance is the creation of point defects such as Ga or N vacancies and subsequent ionization of the traps. We have successfully modeled DC degradation due to radiation effects with FLOODS, a TCAD finite-element simulator. The simulation of trapped negative charges in the GaN buffer layer explained experimental results. As Figure 1 shows, there is a positive shift in threshold voltage that increases with the concentration of negatively charged traps. Another phenomenon that occurs in irradiated AlGaN/GaN HEMTs is an increase in breakdown voltage and apparent enhanced reliability. The fundamental mechanism for this phenomenon is unclear. We have shown that the negatively-trapped charges in the GaN buffer are not the primary mechanism and that charging at the AlGaN surface is a plausible reason. This work explores the fundamental mechanisms for charging of the AlGaN surface. We look at the transient effects of electron and hole creation during radiation and subsequent interfacial trapping mechanisms. Figure 1. Positive shift in threshold voltage with respect to trap concentration in GaN buffer layer.

Research paper thumbnail of Processing Challenges for GaN-Based Photonic and Electronic Devices

MRS Proceedings, 1997

ABSTRACTThe wide gap materials SiC, GaN and to a lesser extent diamond are attracting great inter... more ABSTRACTThe wide gap materials SiC, GaN and to a lesser extent diamond are attracting great interest for high power/high temperature electronics. There are a host of device processing challenges presented by these materials because of their physical and chemical stability, including difficulty in achieving stable, low contact resistances, especially for one conductivity type, absence of convenient wet etch recipes, generally slow dry etch rates, the high temperatures needed for implant activation, control of suitable gate dielectrics and the lack of cheap, large diameter conducting and semi-insulating substrates. The relatively deep ionization levels of some of the common dopants (Mg in GaN; B, Al in SiC; P in diamond) means that carrier densities may be low at room temperature even if the impurity is electrically active - this problem will be reduced at elevated temperature, and thus contact resistances will be greatly improved provided the metallization is stable and reliable. Som...

Research paper thumbnail of Simulation of GaN/AlGaN heterojunction bipolar transistors: part I – npn structures

Solid-State Electronics, 2000

A drift-diffusion model was employed to calculate the dc performance of GaN/AlGaN heterojunction ... more A drift-diffusion model was employed to calculate the dc performance of GaN/AlGaN heterojunction bipolar transistors (HBTs). The dc current gain was found to vary from ∼7 to 60 for collector currents of 10−12–10−2 A in 100 μm contact diameter devices with 2000 Å thick p-GaN base layers (P=2×1017cm−3). The effects of base grading, base thickness, minority carrier lifetime and mobility

Research paper thumbnail of Annealing temperature stability of Ir and Ni-based Ohmic contacts on AlGaN∕GaN high electron mobility transistors

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004

... BPLuther, SEMohney, TNJackson, M.Asif Khan, Q.Chen, and JWYang, “Investigation of the mechani... more ... BPLuther, SEMohney, TNJackson, M.Asif Khan, Q.Chen, and JWYang, “Investigation of the mechanism for Ohmic contact formation in Al and Ti/Al contacts to [bold n]-type GaN,” Appl. Phys. Lett. 70, 57 (1997). Z.Fan, S.Noor Mohammad, W.Kim, Ö.Aktas, AEBotchkarev, and H ...

Research paper thumbnail of GaN enhancement mode metal-oxide semiconductor field effect transistors

physica status solidi (c), 2005

The initial demonstration of an enhancement mode MgO/p-GaN metal-oxide semiconductor field effect... more The initial demonstration of an enhancement mode MgO/p-GaN metal-oxide semiconductor field effect transistor (MOSFET) utilizing Si + ion implanted regions under the source and drain to provide a source of minority carriers for inversion was reported. The breakdown voltage for an 80 nm thick MgO gate dielectric was ~14 V, corresponding to a breakdown field strength of 1.75 MVcm-1 and the p-n junction formed between the p-epi and the source had a reverse breakdown voltage >15 V. Inversion of the channel was achieved for gate voltages above 6 V.The maximum transconductance was 5.4 µSmm-1 at a drain-source voltage of 5 V.

Research paper thumbnail of Study of radiation induced resistance mechanisms in GaAs MESFET and TLM structures

Solid-State Electronics, 2001

The effects of λ-ray irradiation on GaAs MESFETs were studied. The λ-ray irradiation was generate... more The effects of λ-ray irradiation on GaAs MESFETs were studied. The λ-ray irradiation was generated from a 60Co source. DC characteristics of the MESFETs were used to monitor the effects of radiation, which included source–drain I–V characteristics, gate leakage current, saturation drain current, sub-threshold gate leakage current, and sheet resistance. These changes of device characteristics provided us a useful method

Research paper thumbnail of Transmission electron microscopy characterization of electrically stressed AlGaN/GaN high electron mobility transistor devices

Research paper thumbnail of Processing and Device Performance of GaN Power Rectifiers

MRS Proceedings, 1999

Mesa and planar geometry GaN Schottky rectifiers were fabricated on 3-12µm thick epitaxial layers... more Mesa and planar geometry GaN Schottky rectifiers were fabricated on 3-12µm thick epitaxial layers. In planar diodes utilizing resistive GaN, a reverse breakdown voltage of 3.1 kV was achieved in structures containing p-guard rings and employing extension of the Schottky contact edge over an oxide layer. In devices without edge termination, the reverse breakdown voltage was 2.3 kV. Mesa diodes fabricated on conducting GaN had breakdown voltages in the range 200-400 V, with on-state resistances as low as 6m Ωcm−2.

Research paper thumbnail of ZnO-based nanowires

Nano, 2007

ZnO has properties well-suited to UV/visible light emitters, transparent thin film electronics an... more ZnO has properties well-suited to UV/visible light emitters, transparent thin film electronics and a variety of gas and chemical sensor applications. There has been extensive interest in recent times in synthesis of ZnO nanowires by a number of methods using both catalyst and catalyst-free approaches. In this paper we review our recent results on developing functional nanowires in the ZnMgO systems and show some applications in hydrogen gas sensing, pH sensing, transparent transistors and UV detectors. In terms of sensors, the main selling points are large surface-to-volume ratio for improved detection sensitivity and also low power requirements.

Research paper thumbnail of Effects of 2 MeV Ge+ irradiation on AlGaN/GaN high electron mobility transistors

Journal of Vacuum Science & Technology B, 2013

The dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were measured befo... more The dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were measured before and after irradiation with 2 MeV Ge þ ions at doses from 5 Â 10 10 to 5 Â 10 12 cm À2. The drain current, gate leakage current, and transconductance decreased monotonically with dose, while the drain-source resistance increased to a much greater extent than observed previously for proton irradiation of similar devices. The data are consistent with a strong decrease in electron concentration in the HEMT channel. During off-state electrical stressing of AlGaN/GaN HEMTs, the typical critical voltage for unirradiated devices was $13 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 35 V, indicating that the Ge irradiation had a strong influence on the electric field distribution near the gate electrode. V

Research paper thumbnail of Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

Journal of Vacuum Science & Technology B, 2013

ABSTRACT AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffe... more ABSTRACT AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 μm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were ∼100 V, however, this degraded to 50–60 V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600–700 V), while a much smaller Viso of ∼200 V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

Research paper thumbnail of High temperature annealing of GaN, InN, AlN and related alloys

Solid-State Electronics, 1997

Transient thermal processing is employed for implant activation, contact alloying, implant isolat... more Transient thermal processing is employed for implant activation, contact alloying, implant isolation and dehydrogenation during III-nitride device fabrication. We have compared use of InN and AlN powder as methods for providing a N2 partial pressure within a graphite susceptor for high temperature annealing of GaN, InN AlN, InAlN and InGaN. The AlN powder provides adequate surface protection to temperatures of

Research paper thumbnail of High-Density Plasma-Induced Etch Damage of GaN

MRS Proceedings, 1999

ABSTRACTAnisotropic, smooth etching of the group-Ill nitrides has been reported at relatively hig... more ABSTRACTAnisotropic, smooth etching of the group-Ill nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high dc-bias and/or high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional III–V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in shee...

Research paper thumbnail of GaN High Power Devices

… devices for wireless …, 2000

... AP Zhang, 2 G. Dang, 2 XA Cao, 7 KP Lee, 1 H. Cho,'BP Gila,'JW Johnson, 2 C. Monier,&... more ... AP Zhang, 2 G. Dang, 2 XA Cao, 7 KP Lee, 1 H. Cho,'BP Gila,'JW Johnson, 2 C. Monier,'CR Abemathy, 1 J. Han," AG Baca," J.-I ... The figure-of-merit (Vb) 2/Ron was 6.8 MW-cm'2. As the guard-ring width was increased, we observed a monotonic increase in VB, reaching a value of ...

Research paper thumbnail of Self-aligned process for emitter- and base-regrowth GaN HBTs and BJTs

Solid-State Electronics, 2001

The development of a self-aligned fabrication process for small emitter contact area (2×4μm2) GaN... more The development of a self-aligned fabrication process for small emitter contact area (2×4μm2) GaN/AlGaN heterojunction bipolar transistors and GaN bipolar junction transistors is described. The process features dielectric-spacer sidewalls, low damage dry etching and selected-area regrowth of p-GaAs(C) on the base contact or n-GaN/AlGaN on the emitter contact. Series resistance effects are still found to influence the device performance.

Research paper thumbnail of Comparison of ohmic contact properties on n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions

Solid-State Electronics, 2002

GaN/SiC and Al0.25Ga0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic cont... more GaN/SiC and Al0.25Ga0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic contact to the SiC and Ti/Al/Pt/Au for n-ohmic contact to the GaN and AlGaN. Annealing at 850 °C for 20 s (GaN) or 120 s (AlGaN) was required for achieving specific contact resistances in the 10−6Ωcm2 range. The reverse breakdown voltage showed a negative temperature coefficient in both types of sample, with value ∼5.5±2.5×10−3 V/K. The I–V characteristics of both heterojunctions show evidence of tunneling via defect states.

Research paper thumbnail of The effect of N2 plasma damage on AlGaAs/InGaAs/GaAs high electron mobility transistors. I. DC characteristics

Solid-State Electronics, 2000

0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were expo... more 0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were exposed to inductively coupled plasma (ICP) N2 discharges at varied source power and rf chuck power. The plasma damage was characterized by evaluating device extrinsic transconductance and saturated drain–source current, as well as Schottky gate ideality factor and reverse breakdown voltage as a function of both ICP source power

Research paper thumbnail of Surface and bulk leakage currents in high breakdown GaN rectifiers

Solid-State Electronics, 2000

GaN Schottky diode recti®ers with contact diameters 125±1100 mm were fabricated on thick (4 mm) e... more GaN Schottky diode recti®ers with contact diameters 125±1100 mm were fabricated on thick (4 mm) epi layers. At low reverse bias voltages the leakage current was proportional to contact perimeter size while at voltages approximately half the breakdown value, the reverse current was proportional to contact area. These results suggest that surface leakage dominated at low biases, while at higher biases the main contribution was from bulk leakage. The reverse leakage currents were several orders of magnitude higher than the theoretical values, while the forward turn-on voltages were approximately a factor of two higher than the theoretical value.

Research paper thumbnail of Uniformity of dc and rf performance of MBE-grown AlGaN/GaN HEMTS on HVPE-grown buffers

Solid-State Electronics, 2003

AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) o... more AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) on 2 in. diameter GaN buffer layers grown by hydride vapor epitaxy (HVPE) on sapphire substrates. HEMTs with 1 μm gate length displayed excellent dc and rf performance uniformity with up to 258 separate devices measured for each parameter. The drain–source saturation current was 561 mA with

Research paper thumbnail of Conduction mechanisms in W and WSix ohmic contacts to InGaN and InN

Solid-State Electronics, 1997

The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0... more The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0.65Ga0.35N and InN was measured in the range −50–125°C. The results were compared to theoretical values for different conduction mechanisms, to further elucidate the conduction mechanism in these contact structures. The data indicates the conduction mechanism is field emission for these contact schemes for all

Research paper thumbnail of (Invited) Fundamental Modeling of Radiation Effects in AlGaN/GaN HEMTs

ECS Transactions, 2014

ABSTRACT AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They ... more ABSTRACT AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They are also well suited for high power and high frequency applications and thus may be advantageous for satellite-based communication systems. Radiation studies have shown the following DC performance changes: threshold voltage shift (positive), transconductance reduction, and saturation drain current reduction. The basic phenomenon leading to degradation of DC performance is the creation of point defects such as Ga or N vacancies and subsequent ionization of the traps. We have successfully modeled DC degradation due to radiation effects with FLOODS, a TCAD finite-element simulator. The simulation of trapped negative charges in the GaN buffer layer explained experimental results. As Figure 1 shows, there is a positive shift in threshold voltage that increases with the concentration of negatively charged traps. Another phenomenon that occurs in irradiated AlGaN/GaN HEMTs is an increase in breakdown voltage and apparent enhanced reliability. The fundamental mechanism for this phenomenon is unclear. We have shown that the negatively-trapped charges in the GaN buffer are not the primary mechanism and that charging at the AlGaN surface is a plausible reason. This work explores the fundamental mechanisms for charging of the AlGaN surface. We look at the transient effects of electron and hole creation during radiation and subsequent interfacial trapping mechanisms. Figure 1. Positive shift in threshold voltage with respect to trap concentration in GaN buffer layer.

Research paper thumbnail of Processing Challenges for GaN-Based Photonic and Electronic Devices

MRS Proceedings, 1997

ABSTRACTThe wide gap materials SiC, GaN and to a lesser extent diamond are attracting great inter... more ABSTRACTThe wide gap materials SiC, GaN and to a lesser extent diamond are attracting great interest for high power/high temperature electronics. There are a host of device processing challenges presented by these materials because of their physical and chemical stability, including difficulty in achieving stable, low contact resistances, especially for one conductivity type, absence of convenient wet etch recipes, generally slow dry etch rates, the high temperatures needed for implant activation, control of suitable gate dielectrics and the lack of cheap, large diameter conducting and semi-insulating substrates. The relatively deep ionization levels of some of the common dopants (Mg in GaN; B, Al in SiC; P in diamond) means that carrier densities may be low at room temperature even if the impurity is electrically active - this problem will be reduced at elevated temperature, and thus contact resistances will be greatly improved provided the metallization is stable and reliable. Som...

Research paper thumbnail of Simulation of GaN/AlGaN heterojunction bipolar transistors: part I – npn structures

Solid-State Electronics, 2000

A drift-diffusion model was employed to calculate the dc performance of GaN/AlGaN heterojunction ... more A drift-diffusion model was employed to calculate the dc performance of GaN/AlGaN heterojunction bipolar transistors (HBTs). The dc current gain was found to vary from ∼7 to 60 for collector currents of 10−12–10−2 A in 100 μm contact diameter devices with 2000 Å thick p-GaN base layers (P=2×1017cm−3). The effects of base grading, base thickness, minority carrier lifetime and mobility

Research paper thumbnail of Annealing temperature stability of Ir and Ni-based Ohmic contacts on AlGaN∕GaN high electron mobility transistors

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004

... BPLuther, SEMohney, TNJackson, M.Asif Khan, Q.Chen, and JWYang, “Investigation of the mechani... more ... BPLuther, SEMohney, TNJackson, M.Asif Khan, Q.Chen, and JWYang, “Investigation of the mechanism for Ohmic contact formation in Al and Ti/Al contacts to [bold n]-type GaN,” Appl. Phys. Lett. 70, 57 (1997). Z.Fan, S.Noor Mohammad, W.Kim, Ö.Aktas, AEBotchkarev, and H ...

Research paper thumbnail of GaN enhancement mode metal-oxide semiconductor field effect transistors

physica status solidi (c), 2005

The initial demonstration of an enhancement mode MgO/p-GaN metal-oxide semiconductor field effect... more The initial demonstration of an enhancement mode MgO/p-GaN metal-oxide semiconductor field effect transistor (MOSFET) utilizing Si + ion implanted regions under the source and drain to provide a source of minority carriers for inversion was reported. The breakdown voltage for an 80 nm thick MgO gate dielectric was ~14 V, corresponding to a breakdown field strength of 1.75 MVcm-1 and the p-n junction formed between the p-epi and the source had a reverse breakdown voltage >15 V. Inversion of the channel was achieved for gate voltages above 6 V.The maximum transconductance was 5.4 µSmm-1 at a drain-source voltage of 5 V.

Research paper thumbnail of Study of radiation induced resistance mechanisms in GaAs MESFET and TLM structures

Solid-State Electronics, 2001

The effects of λ-ray irradiation on GaAs MESFETs were studied. The λ-ray irradiation was generate... more The effects of λ-ray irradiation on GaAs MESFETs were studied. The λ-ray irradiation was generated from a 60Co source. DC characteristics of the MESFETs were used to monitor the effects of radiation, which included source–drain I–V characteristics, gate leakage current, saturation drain current, sub-threshold gate leakage current, and sheet resistance. These changes of device characteristics provided us a useful method

Research paper thumbnail of Transmission electron microscopy characterization of electrically stressed AlGaN/GaN high electron mobility transistor devices

Research paper thumbnail of Processing and Device Performance of GaN Power Rectifiers

MRS Proceedings, 1999

Mesa and planar geometry GaN Schottky rectifiers were fabricated on 3-12µm thick epitaxial layers... more Mesa and planar geometry GaN Schottky rectifiers were fabricated on 3-12µm thick epitaxial layers. In planar diodes utilizing resistive GaN, a reverse breakdown voltage of 3.1 kV was achieved in structures containing p-guard rings and employing extension of the Schottky contact edge over an oxide layer. In devices without edge termination, the reverse breakdown voltage was 2.3 kV. Mesa diodes fabricated on conducting GaN had breakdown voltages in the range 200-400 V, with on-state resistances as low as 6m Ωcm−2.

Research paper thumbnail of ZnO-based nanowires

Nano, 2007

ZnO has properties well-suited to UV/visible light emitters, transparent thin film electronics an... more ZnO has properties well-suited to UV/visible light emitters, transparent thin film electronics and a variety of gas and chemical sensor applications. There has been extensive interest in recent times in synthesis of ZnO nanowires by a number of methods using both catalyst and catalyst-free approaches. In this paper we review our recent results on developing functional nanowires in the ZnMgO systems and show some applications in hydrogen gas sensing, pH sensing, transparent transistors and UV detectors. In terms of sensors, the main selling points are large surface-to-volume ratio for improved detection sensitivity and also low power requirements.

Research paper thumbnail of Effects of 2 MeV Ge+ irradiation on AlGaN/GaN high electron mobility transistors

Journal of Vacuum Science & Technology B, 2013

The dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were measured befo... more The dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were measured before and after irradiation with 2 MeV Ge þ ions at doses from 5 Â 10 10 to 5 Â 10 12 cm À2. The drain current, gate leakage current, and transconductance decreased monotonically with dose, while the drain-source resistance increased to a much greater extent than observed previously for proton irradiation of similar devices. The data are consistent with a strong decrease in electron concentration in the HEMT channel. During off-state electrical stressing of AlGaN/GaN HEMTs, the typical critical voltage for unirradiated devices was $13 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 35 V, indicating that the Ge irradiation had a strong influence on the electric field distribution near the gate electrode. V

Research paper thumbnail of Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

Journal of Vacuum Science & Technology B, 2013

ABSTRACT AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffe... more ABSTRACT AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 μm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were ∼100 V, however, this degraded to 50–60 V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600–700 V), while a much smaller Viso of ∼200 V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

Research paper thumbnail of High temperature annealing of GaN, InN, AlN and related alloys

Solid-State Electronics, 1997

Transient thermal processing is employed for implant activation, contact alloying, implant isolat... more Transient thermal processing is employed for implant activation, contact alloying, implant isolation and dehydrogenation during III-nitride device fabrication. We have compared use of InN and AlN powder as methods for providing a N2 partial pressure within a graphite susceptor for high temperature annealing of GaN, InN AlN, InAlN and InGaN. The AlN powder provides adequate surface protection to temperatures of

Research paper thumbnail of High-Density Plasma-Induced Etch Damage of GaN

MRS Proceedings, 1999

ABSTRACTAnisotropic, smooth etching of the group-Ill nitrides has been reported at relatively hig... more ABSTRACTAnisotropic, smooth etching of the group-Ill nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high dc-bias and/or high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional III–V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in shee...

Research paper thumbnail of GaN High Power Devices

… devices for wireless …, 2000

... AP Zhang, 2 G. Dang, 2 XA Cao, 7 KP Lee, 1 H. Cho,'BP Gila,'JW Johnson, 2 C. Monier,&... more ... AP Zhang, 2 G. Dang, 2 XA Cao, 7 KP Lee, 1 H. Cho,'BP Gila,'JW Johnson, 2 C. Monier,'CR Abemathy, 1 J. Han," AG Baca," J.-I ... The figure-of-merit (Vb) 2/Ron was 6.8 MW-cm'2. As the guard-ring width was increased, we observed a monotonic increase in VB, reaching a value of ...

Research paper thumbnail of Self-aligned process for emitter- and base-regrowth GaN HBTs and BJTs

Solid-State Electronics, 2001

The development of a self-aligned fabrication process for small emitter contact area (2×4μm2) GaN... more The development of a self-aligned fabrication process for small emitter contact area (2×4μm2) GaN/AlGaN heterojunction bipolar transistors and GaN bipolar junction transistors is described. The process features dielectric-spacer sidewalls, low damage dry etching and selected-area regrowth of p-GaAs(C) on the base contact or n-GaN/AlGaN on the emitter contact. Series resistance effects are still found to influence the device performance.

Research paper thumbnail of Comparison of ohmic contact properties on n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions

Solid-State Electronics, 2002

GaN/SiC and Al0.25Ga0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic cont... more GaN/SiC and Al0.25Ga0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic contact to the SiC and Ti/Al/Pt/Au for n-ohmic contact to the GaN and AlGaN. Annealing at 850 °C for 20 s (GaN) or 120 s (AlGaN) was required for achieving specific contact resistances in the 10−6Ωcm2 range. The reverse breakdown voltage showed a negative temperature coefficient in both types of sample, with value ∼5.5±2.5×10−3 V/K. The I–V characteristics of both heterojunctions show evidence of tunneling via defect states.

Research paper thumbnail of The effect of N2 plasma damage on AlGaAs/InGaAs/GaAs high electron mobility transistors. I. DC characteristics

Solid-State Electronics, 2000

0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were expo... more 0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were exposed to inductively coupled plasma (ICP) N2 discharges at varied source power and rf chuck power. The plasma damage was characterized by evaluating device extrinsic transconductance and saturated drain–source current, as well as Schottky gate ideality factor and reverse breakdown voltage as a function of both ICP source power

Research paper thumbnail of Surface and bulk leakage currents in high breakdown GaN rectifiers

Solid-State Electronics, 2000

GaN Schottky diode recti®ers with contact diameters 125±1100 mm were fabricated on thick (4 mm) e... more GaN Schottky diode recti®ers with contact diameters 125±1100 mm were fabricated on thick (4 mm) epi layers. At low reverse bias voltages the leakage current was proportional to contact perimeter size while at voltages approximately half the breakdown value, the reverse current was proportional to contact area. These results suggest that surface leakage dominated at low biases, while at higher biases the main contribution was from bulk leakage. The reverse leakage currents were several orders of magnitude higher than the theoretical values, while the forward turn-on voltages were approximately a factor of two higher than the theoretical value.

Research paper thumbnail of Uniformity of dc and rf performance of MBE-grown AlGaN/GaN HEMTS on HVPE-grown buffers

Solid-State Electronics, 2003

AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) o... more AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) on 2 in. diameter GaN buffer layers grown by hydride vapor epitaxy (HVPE) on sapphire substrates. HEMTs with 1 μm gate length displayed excellent dc and rf performance uniformity with up to 258 separate devices measured for each parameter. The drain–source saturation current was 561 mA with