A. Christou - Academia.edu (original) (raw)

Papers by A. Christou

Research paper thumbnail of Redistribution of aluminum in MODFET ohmic contacts

Solid-State Electronics, 1986

ABSTRACT

Research paper thumbnail of Surface related failure mechanisms in polyimide passivated L-band MMICs

31st Annual Proceedings Reliability Physics 1993, 1993

ABSTRACT

Research paper thumbnail of Point defect recovery of shock deformed iron alloys

Scripta Metallurgica, 1971

Research paper thumbnail of Tunable wavelength surface quantum cascade lasers for chemical sensors in the 3-6 μm spectral region

SPIE Proceedings, 2007

The authors present the design and calculated performance of a low threshold selectively oxidized... more The authors present the design and calculated performance of a low threshold selectively oxidized Surface Emitting Laser (SEL) for operation at a wavelength of up 3.0 mum. The device is based on III-V quaternary semiconductor alloys and is grown by the Molecular Beam Epitaxy technique. The theoretical investigation of the optical properties of the compound semiconductor alloys allows for the selection of the optimum materials for highly reflective Bragg mirrors. The simulation of the designed SEL performance has been carried out by evaluation of the important laser characteristics such as threshold gain, threshold current density and external quantum efficiency. We present a design which integrates a thermoelectric controller and multi-SELs to provide continuous tunability.

Research paper thumbnail of Evaluation of promising alternative a-Si deposition methods

Photovoltaic Power Generation, 1988

Research paper thumbnail of GaInSbAs/AlInSbAs vertical-cavity surface-emitting laser (VCSEL) for operation at 1.5 μm

Physics and Simulation of Optoelectronic Devices VII, 1999

ABSTRACT

Research paper thumbnail of Optical interconnect reliability

Optical Engineering, 1998

In order to make appropriate technology choices for the system implementation of optical intercon... more In order to make appropriate technology choices for the system implementation of optical interconnects, the issues of reliability and manufacturability must be included in any figure of merit (FOM) calculation.

Research paper thumbnail of Failure mechanisms of GaAs mesfets with Cu/refractory metallized gates

Microelectronics Reliability, 1997

The DC performance of Cu-based GaAs MESFETs with Au/Cu/Ti and Cu/TiW metallized gates has been ch... more The DC performance of Cu-based GaAs MESFETs with Au/Cu/Ti and Cu/TiW metallized gates has been characterized after accelerated stress testing up to 250°C and anneals of 1000 hours. A failure mode has been shown to result in a decrease in I DSS , g m and V P and ...

Research paper thumbnail of A new failure mechanism in thin gold films at elevated temperatures

Microelectronics Journal, 1984

Research paper thumbnail of Epitaxial issues and growth morphologies of InAlAs/InGaAs heterostructures on non-(100) InP index substrates

Materials Science and Engineering: B, 2001

ABSTRACT

Research paper thumbnail of Defect formation in SiGe/Si structures grown on GaAs by CVD techniques utilizing a Si:H template layer

Materials Science and Engineering: B, 1999

Epitaxial SiGe layers and Si/SiGe modulated heterostructures were successfully grown on GaAs subs... more Epitaxial SiGe layers and Si/SiGe modulated heterostructures were successfully grown on GaAs substrates by chemical vapor deposition (CVD) techniques utilizing an amorphous-Si:H buffer layer as a transition layer between SiGe and GaAs. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to investigate the structural quality of the SiGe layers on GaAs. It was shown that the amorphous transition layer of silicon resulted in an initial 2D epitaxial growth of SiGe films on GaAs. However, the SiGe films were found to be strained and threading dislocations were observed. Traps in SiGe films were identified to be mainly minority type at 0.15-0.20 eV, in addition to the two majority traps at 0.25 and 0.46 eV. The DC characteristics of SiGe Schottky diodes on GaAs substrates were also measured, and showed that the barrier height varied from 0.35 to 0.85 eV depending on the Ge concentration.

Research paper thumbnail of High mobility GaAs/AlAs/(211)Si structures grown by MBE

Journal of Crystal Growth, 1987

The growth on the preferred (211) silicon surface has been accomplished utilizing an interfacial ... more The growth on the preferred (211) silicon surface has been accomplished utilizing an interfacial layer of 100 A of AlAs. We report on the (i) surface preparation, (ii) arsenic rich growth and (iii) mobility measurements of the resultant GaAs/AIA5(211) Si structure. An arsenic rich initial growth was utilized, which resulted in a sharp 2~'<2 reconstructed GaAs surface. In comparison, a gallium rich surface resulted in antiphase domains and in worst case Ga rich modules. Surface oxides were desorbed at 800°prior to deposition at a final substrate temperature of 600-610°Cfor GaAs and 700°Cfor AlAs. The deposition in both cases was initiated at 250°C. Undoped GaAs/AIAs/(211) Si structures resulted in room temperature mobility values of 5275-8000 cm 2/Vs. The mobility values were optimizing by varying the thickness of the AlAs. A thickness of 100-120 A was found to be necessary to prevent compensation due to outdiffusion from the silicon substrate. The GaAs films were shown to be smooth without evidence of antiphase domains.

Research paper thumbnail of Electric field dependence of allowed and forbidden transitions in In0.53Ga0.47As/In0.52Al0.48As single quantum wells by room temperature modulation spectroscopy

Applied Surface Science, 1993

ABSTRACT

Research paper thumbnail of Electrical transport study of pseudomorphic heterostructures InGaAs-InAlAs on Si and InP substrates

Sensors and Actuators A: Physical, 1992

ABSTRACT

Research paper thumbnail of High Temperature Performance, Reliability and Simulation of GaAs Mesfets with CVD Diamond Heat Sinks

MRS Proceedings, 1992

ABSTRACTAn investigation of the temperature stability and high temperature characteristics of GaA... more ABSTRACTAn investigation of the temperature stability and high temperature characteristics of GaAs FETs on CVD diamond heat sinks was carried out by modeling the high temperature electrical characteristics for GaAs MESFETs and by experimentally measuring the elevated temperature performance. The thermal characteristics were determined experimentally using infrared microscopy techniques. The thermal measurements by infrared microscopy were correlated with results of a finite element analysis calculation of the GaAs FET thermal distribution. Reliability testing at 230°C resulted in an MTF of approximately 2000 hours.

Research paper thumbnail of TiNi/GaAs Thin Film Structures for Gate Metallizations

MRS Proceedings, 2000

Shape memory alloy TiNi thin films on GaAs have been investigated. A series of TiNi compositions ... more Shape memory alloy TiNi thin films on GaAs have been investigated. A series of TiNi compositions were electron beam deposited on GaAs initially as thin multilayers of Ti and Ni. The intermetallic phase of TiNi was formed by annealing and complete intermixing of the multilayers at 370oC. The intermetallic phases were investigated with X-ray diffraction techniques. The annealing kinetics and resistivity investigations were carried out in order to minimize the sheet resistance of the intermetallic phase. TiNi Schottky barriers on GaAs have been fabricated and their performance will be reported. Additional investigations on surface morphology using the energy dispersive spectroscopy as well as TEM investigations show the correlation between microstructure, intermetallic phase formation and sheet resistance.

Research paper thumbnail of Asymmetric Fabry-Perot p-i-n multiple quantum well optical modulators grown on silicon and GaAs substrates

Superlattices and Microstructures, 1992

In the present work, GaAs/AlGaAs multiple quantum well p-in optical modulators were fabricated on... more In the present work, GaAs/AlGaAs multiple quantum well p-in optical modulators were fabricated on Si (MQW/Si) and GaAs (MQW/GaAs) substrates. Although an ap preciable red Stark shift was observed with an applied reverse bias, a rather low reflection modulation (limited to changes of only a few percent) was obtained. Nevertheless, successful operation of the MQW/Si device as a light modulator is demonstrated using a-5 V square wave drive at 1.5 kHz. A negative differential photoconductivity region exhibited by the MQW/Si structure may lead to optical bistability in the future, provided the p-in diode characteristics are improved.

Research paper thumbnail of Charge control in a Laser Processed superlattice High Electron Mobility Transistor (LPHEMT)

Solid-State Electronics, 1989

ABSTRACT

Research paper thumbnail of Subsurface burnout mechanisms in gallium arsenide (GAAS) electronic devices

Quality and Reliability Engineering International, 1988

ABSTRACT

Research paper thumbnail of Optical properties of GaAs1−xNxalloys grown by molecular beam epitaxy

Philosophical Magazine, 2006

Optical properties of GaAs 1Àx N x alloys grown by molecular beam epitaxy using GaAs (001) as the... more Optical properties of GaAs 1Àx N x alloys grown by molecular beam epitaxy using GaAs (001) as the substrate have been studied. These include photoluminescence (PL), cathodoluminescence (CL), photocurrent and photomemory effects. The low-temperature (77 K) PL characteristics were measured on samples with 0-0.105% N content. The wide emission band indicates the defective nature of the materials. The widening of the band for materials with increasing nitrogen concentration also suggested that the concentration of defect states in these materials dramatically increased with increasing nitrogen content. The PL and CL spectra for GaAs 1Àx N x layer 1854 did not show identical characteristics. Some layers showed a very sharp fall in photocurrent at low temperatures, indicating a very sharp photoquenching and an interaction between antisite, interstitial and vacancy defects. The photomemory effect, which causes photoquenching and the transition from the EL2 to the EL2* metastable state, was strongly influenced by the optical exposure and thermal history of the sample.

Research paper thumbnail of Redistribution of aluminum in MODFET ohmic contacts

Solid-State Electronics, 1986

ABSTRACT

Research paper thumbnail of Surface related failure mechanisms in polyimide passivated L-band MMICs

31st Annual Proceedings Reliability Physics 1993, 1993

ABSTRACT

Research paper thumbnail of Point defect recovery of shock deformed iron alloys

Scripta Metallurgica, 1971

Research paper thumbnail of Tunable wavelength surface quantum cascade lasers for chemical sensors in the 3-6 μm spectral region

SPIE Proceedings, 2007

The authors present the design and calculated performance of a low threshold selectively oxidized... more The authors present the design and calculated performance of a low threshold selectively oxidized Surface Emitting Laser (SEL) for operation at a wavelength of up 3.0 mum. The device is based on III-V quaternary semiconductor alloys and is grown by the Molecular Beam Epitaxy technique. The theoretical investigation of the optical properties of the compound semiconductor alloys allows for the selection of the optimum materials for highly reflective Bragg mirrors. The simulation of the designed SEL performance has been carried out by evaluation of the important laser characteristics such as threshold gain, threshold current density and external quantum efficiency. We present a design which integrates a thermoelectric controller and multi-SELs to provide continuous tunability.

Research paper thumbnail of Evaluation of promising alternative a-Si deposition methods

Photovoltaic Power Generation, 1988

Research paper thumbnail of GaInSbAs/AlInSbAs vertical-cavity surface-emitting laser (VCSEL) for operation at 1.5 μm

Physics and Simulation of Optoelectronic Devices VII, 1999

ABSTRACT

Research paper thumbnail of Optical interconnect reliability

Optical Engineering, 1998

In order to make appropriate technology choices for the system implementation of optical intercon... more In order to make appropriate technology choices for the system implementation of optical interconnects, the issues of reliability and manufacturability must be included in any figure of merit (FOM) calculation.

Research paper thumbnail of Failure mechanisms of GaAs mesfets with Cu/refractory metallized gates

Microelectronics Reliability, 1997

The DC performance of Cu-based GaAs MESFETs with Au/Cu/Ti and Cu/TiW metallized gates has been ch... more The DC performance of Cu-based GaAs MESFETs with Au/Cu/Ti and Cu/TiW metallized gates has been characterized after accelerated stress testing up to 250°C and anneals of 1000 hours. A failure mode has been shown to result in a decrease in I DSS , g m and V P and ...

Research paper thumbnail of A new failure mechanism in thin gold films at elevated temperatures

Microelectronics Journal, 1984

Research paper thumbnail of Epitaxial issues and growth morphologies of InAlAs/InGaAs heterostructures on non-(100) InP index substrates

Materials Science and Engineering: B, 2001

ABSTRACT

Research paper thumbnail of Defect formation in SiGe/Si structures grown on GaAs by CVD techniques utilizing a Si:H template layer

Materials Science and Engineering: B, 1999

Epitaxial SiGe layers and Si/SiGe modulated heterostructures were successfully grown on GaAs subs... more Epitaxial SiGe layers and Si/SiGe modulated heterostructures were successfully grown on GaAs substrates by chemical vapor deposition (CVD) techniques utilizing an amorphous-Si:H buffer layer as a transition layer between SiGe and GaAs. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to investigate the structural quality of the SiGe layers on GaAs. It was shown that the amorphous transition layer of silicon resulted in an initial 2D epitaxial growth of SiGe films on GaAs. However, the SiGe films were found to be strained and threading dislocations were observed. Traps in SiGe films were identified to be mainly minority type at 0.15-0.20 eV, in addition to the two majority traps at 0.25 and 0.46 eV. The DC characteristics of SiGe Schottky diodes on GaAs substrates were also measured, and showed that the barrier height varied from 0.35 to 0.85 eV depending on the Ge concentration.

Research paper thumbnail of High mobility GaAs/AlAs/(211)Si structures grown by MBE

Journal of Crystal Growth, 1987

The growth on the preferred (211) silicon surface has been accomplished utilizing an interfacial ... more The growth on the preferred (211) silicon surface has been accomplished utilizing an interfacial layer of 100 A of AlAs. We report on the (i) surface preparation, (ii) arsenic rich growth and (iii) mobility measurements of the resultant GaAs/AIA5(211) Si structure. An arsenic rich initial growth was utilized, which resulted in a sharp 2~'<2 reconstructed GaAs surface. In comparison, a gallium rich surface resulted in antiphase domains and in worst case Ga rich modules. Surface oxides were desorbed at 800°prior to deposition at a final substrate temperature of 600-610°Cfor GaAs and 700°Cfor AlAs. The deposition in both cases was initiated at 250°C. Undoped GaAs/AIAs/(211) Si structures resulted in room temperature mobility values of 5275-8000 cm 2/Vs. The mobility values were optimizing by varying the thickness of the AlAs. A thickness of 100-120 A was found to be necessary to prevent compensation due to outdiffusion from the silicon substrate. The GaAs films were shown to be smooth without evidence of antiphase domains.

Research paper thumbnail of Electric field dependence of allowed and forbidden transitions in In0.53Ga0.47As/In0.52Al0.48As single quantum wells by room temperature modulation spectroscopy

Applied Surface Science, 1993

ABSTRACT

Research paper thumbnail of Electrical transport study of pseudomorphic heterostructures InGaAs-InAlAs on Si and InP substrates

Sensors and Actuators A: Physical, 1992

ABSTRACT

Research paper thumbnail of High Temperature Performance, Reliability and Simulation of GaAs Mesfets with CVD Diamond Heat Sinks

MRS Proceedings, 1992

ABSTRACTAn investigation of the temperature stability and high temperature characteristics of GaA... more ABSTRACTAn investigation of the temperature stability and high temperature characteristics of GaAs FETs on CVD diamond heat sinks was carried out by modeling the high temperature electrical characteristics for GaAs MESFETs and by experimentally measuring the elevated temperature performance. The thermal characteristics were determined experimentally using infrared microscopy techniques. The thermal measurements by infrared microscopy were correlated with results of a finite element analysis calculation of the GaAs FET thermal distribution. Reliability testing at 230°C resulted in an MTF of approximately 2000 hours.

Research paper thumbnail of TiNi/GaAs Thin Film Structures for Gate Metallizations

MRS Proceedings, 2000

Shape memory alloy TiNi thin films on GaAs have been investigated. A series of TiNi compositions ... more Shape memory alloy TiNi thin films on GaAs have been investigated. A series of TiNi compositions were electron beam deposited on GaAs initially as thin multilayers of Ti and Ni. The intermetallic phase of TiNi was formed by annealing and complete intermixing of the multilayers at 370oC. The intermetallic phases were investigated with X-ray diffraction techniques. The annealing kinetics and resistivity investigations were carried out in order to minimize the sheet resistance of the intermetallic phase. TiNi Schottky barriers on GaAs have been fabricated and their performance will be reported. Additional investigations on surface morphology using the energy dispersive spectroscopy as well as TEM investigations show the correlation between microstructure, intermetallic phase formation and sheet resistance.

Research paper thumbnail of Asymmetric Fabry-Perot p-i-n multiple quantum well optical modulators grown on silicon and GaAs substrates

Superlattices and Microstructures, 1992

In the present work, GaAs/AlGaAs multiple quantum well p-in optical modulators were fabricated on... more In the present work, GaAs/AlGaAs multiple quantum well p-in optical modulators were fabricated on Si (MQW/Si) and GaAs (MQW/GaAs) substrates. Although an ap preciable red Stark shift was observed with an applied reverse bias, a rather low reflection modulation (limited to changes of only a few percent) was obtained. Nevertheless, successful operation of the MQW/Si device as a light modulator is demonstrated using a-5 V square wave drive at 1.5 kHz. A negative differential photoconductivity region exhibited by the MQW/Si structure may lead to optical bistability in the future, provided the p-in diode characteristics are improved.

Research paper thumbnail of Charge control in a Laser Processed superlattice High Electron Mobility Transistor (LPHEMT)

Solid-State Electronics, 1989

ABSTRACT

Research paper thumbnail of Subsurface burnout mechanisms in gallium arsenide (GAAS) electronic devices

Quality and Reliability Engineering International, 1988

ABSTRACT

Research paper thumbnail of Optical properties of GaAs1−xNxalloys grown by molecular beam epitaxy

Philosophical Magazine, 2006

Optical properties of GaAs 1Àx N x alloys grown by molecular beam epitaxy using GaAs (001) as the... more Optical properties of GaAs 1Àx N x alloys grown by molecular beam epitaxy using GaAs (001) as the substrate have been studied. These include photoluminescence (PL), cathodoluminescence (CL), photocurrent and photomemory effects. The low-temperature (77 K) PL characteristics were measured on samples with 0-0.105% N content. The wide emission band indicates the defective nature of the materials. The widening of the band for materials with increasing nitrogen concentration also suggested that the concentration of defect states in these materials dramatically increased with increasing nitrogen content. The PL and CL spectra for GaAs 1Àx N x layer 1854 did not show identical characteristics. Some layers showed a very sharp fall in photocurrent at low temperatures, indicating a very sharp photoquenching and an interaction between antisite, interstitial and vacancy defects. The photomemory effect, which causes photoquenching and the transition from the EL2 to the EL2* metastable state, was strongly influenced by the optical exposure and thermal history of the sample.