Metalorganic chemical vapor deposition of AlGaAs and InGaP heterojunction bipolar transistors (original) (raw)
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Japanese Journal of Applied Physics, 2002
InP/InGaAs PNP heterojunction bipolar transistor (HBT) layers have been grown by metalorganic chemical vapor deposition (MOCVD) and devices have been fabricated using a self-aligned processing technology. A zinc-doped InP layer has been employed as the wide-bandgap emitter layer for the PNP HBT. The base layer used a 500Å thick n-type InGaAs layer doped at 5 × 10 18 cm −3. Successful high frequency operation of these devices has been demonstrated. A single-emitter 1 × 20 µm 2 MOCVD-grown PNP InP/InGaAs HBT achieved current gain cutoff frequency (f T) of more than 11 GHz at a current density (J C) of 8.25 × 10 4 A/cm 2 .
High Performance Al0:35Ga0:65As/GaAs HBT’s
AlGaAs emitter heterojunction bipolar transistors (HBT's) are demonstrated to have excellent dc and RF properties comparable to InGaP/GaAs HBT's by increasing the Al composition. Al 0 35 Ga 0 65 As/GaAs HBT's exhibit very high dc current gain at all bias levels, exceeding 140 at 25 A/cm 2 and reaching a maximum of 210 at 26 kA/cm 2 ( = 1 4 m 3 m, = 330 ). The temperature dependence of the peak dc current gain is also significantly improved by increasing the AlGaAs mole fraction of the emitter. Device analysis suggests that a larger emitter energy-gap contributes to the improved device performance by both lowering space charge recombination and increasing the barrier to reverse hole injection.
Solid-State Electronics, 1999
The d.c. and microwave characteristics of graded and abrupt junction In 0.32 Al 0.68 As/In 0.33 Ga 0.67 As heterojunction bipolar transistors (HBTs) grown on GaAs were investigated. A step-graded In x Ga 1 À x As buer was employed to eectively suppress the threading dislocations resulting from the lattice mismatch between In 0.33 Ga 0.67 As and GaAs. These devices exhibited a small turn-on voltage of collector current and a high collector±emitter breakdown voltage (BV CEO >9.5 V) for a 0.35 mm-thick collector, demonstrating excellent quality of the base±emitter and base± collector junctions. Less size-dependence on current gain was observed for these metamorphic HBTs even without the emitter ledge. The peak common-emitter current gain at a collector current density of 40 kA/cm 2 is 53 for the graded junction device with an emitter size of 2 Â 4 mm 2 and a base doping of 2 Â 10 19 cm À3. An F max of 56 GHz was measured for this device.
IEEE Journal of the Electron Devices Society
N-p-n InGaP/GaAs double heterojunction bipolar transistor has been successfully grown on a 200 mm Ge/Si wafer using metalorganic chemical vapor deposition with low defect density of 10 7 cm −2. Non-gold metals of Ni/Ge/Al and Ti/Al are used to form the ohmic contact for small pieces device fabrication. Both direct-current (dc) and high-frequency characteristics of the device were measured. The device with emitter area of 6×8 µm 2 shows a dc gain of 55 at a collector current of I c = 4 mA, with high collector-emitter breakdown voltage of ∼17 V. The high-frequency response with cutoff frequency (f T) of 23 GHz and maximum available frequency (f max) of 10 GHz can be achieved. These results demonstrate that InGaP/GaAs double heterojunction bipolar transistor grown on low defect density Ge/Si wafer has the potential for realizing III-V CMOS integrated platform for high-frequency applications.
Assessment of layer structures for GaInP/GaAs-heterojunction bipolar transistors
Materials Science and Engineering: B, 1999
GaAs-based heterojunction bipolar transistors (HBTs) are expected to take an increasing share of the currently expanding market for mobile communications products. The GaInP/GaAs-system offers advantages for device performance and fabrication in comparison with the already established AlGaAs/GaAs-system. However, HBT fabrication is still not mature technology. The main obstacle is the reproducible supply of high quality HBT epitaxial layer structures. An appropriate evaluation of the HBT layer structures is essential to successfully establish the epitaxial growth technology. The ratio of current gain to base sheet resistance is known to be one of the most meaningful figures of merit for the HBT. Therefore, the development of proper epitaxial growth procedures for HBT layer structures includes a device qualification. To the end of the evaluation of GalnP/GaAs-HBT layer structures we have established a fast HBT process that additionally provides windows for material analysis in different depths of the structure. The fundamental device performance and the wafer uniformity are assessed by dc parameter mapping of large area devices and conventional test structures. Several material diagnostic techniques were applied to assess layer properties. Some of the capabilities of these methods are discussed. Our fast HBT process has been instrumental in the development of GalnP/GaAs HBT layer structures at Epitaxial Products International. Current gain of 161 at the base sheet resistance of 273 V sq − 1 with a standard deviation of the current gain across a 3 in. wafer of 1% proves that these GalnP/GaAs-HBT layer structures are comparable with currently available state-of-the-art AlGaAs/GaAs-HBT layer structures. Parts of the work were performed within the EC-project ESPRIT 21315 GAMMA.
Microelectronics Journal, 2004
This paper presents a comprehensive comparison of three state-of-the-art heterojunction bipolar transistors (HBTs); the AlGaAs/GaAs HBT, the Si/SiGe HBT and the InGaAs/InP HBT. Our aim in this paper is to find the potentials and limitations of these devices and analyze them under common Figure of Merit (FOM) definitions as well as to make a meaningful comparison which is necessary for a technology choice especially in RF-circuit and system level applications such as power amplifier, low noise amplifier circuits and transceiver/receiver systems. Simulation of an HBT device with an HBT model instead of traditional BJT models is also presented for the AlGaAs/GaAs HBT. To the best of our knowledge, this work covers the most extensive FOM analysis for these devices such as I-V behavior, stability, power gain analysis, characteristic frequencies and minimum noise figure. DC and bias point simulations of the devices are performed using Agilent's ADS design tool and a comparison is given for a wide range of FOM specifications. Based on our literature survey and simulation results, we have concluded that GaAs based HBTs are suitable for high-power applications due to their high-breakdown voltages, SiGe based HBTs are promising for low noise applications due to their low noise figures and InP will be the choice if very high-data rates is of primary importance since InP based HBT transistors have superior material properties leading to Terahertz frequency operation. q
AIP Advances
We report performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) fabricated on epitaxial films directly grown onto 200 mm silicon (Si) substrates using a thin 100% germanium (Ge) buffer layer. Both buffer layer and device layers were grown epitaxially using metalorganic chemical vapor deposition (MOCVD). With the assistance of numerical simulation, we were able to achieve high performance GaAs HBTs with DC current gain of ∼100 through optimizing the base doping concentration (C-doped, ∼ 1.9×10 19 /cm 3), base layer thickness (∼55 nm), and the sub-collector doping concentration (Te-doped, > 5×10 18 /cm 3). The breakdown voltage at base (BV ceo) of higher than 9.43 V was realized with variation of < 3% across the 200 mm wafer. These results could enable applications such as power amplifiers for mobile phone handsets and monolithic integration of HBTs with standard Si-CMOS transistors on a common Si platform.
GaAs Heterojunction Bipolar Transistor Emitter Design
We demonstrate that GaAs-based HBTs with very low base currents at both low and high injection levels can be achieved using either Al 0.35 Ga 0.65 As or InGaP in the emitter with the proper optimization of structure and growth. We observe an order of magnitude reduction in space charge recombination current as the Al composition, and hence the energy-gap, of the emitter increases from 25% (1.77 eV) to 35% (1.89 eV). AlGaAs/GaAs HBTs with approximately 35% Al have the same energy-gap as InGaP and exhibit comparable space charge recombination in large area devices (L = 75 x 75 µm 2 ). Moreover, this reduction in the space charge recombination in Al 0.35 Ga 0.65 As/GaAs HBTs can be achieved while maintaining a low turn-on voltage and high DC current gain over a wide range of current densities. Small area devices (L = 1.4 x 3 µm 2 ) fabricated with an Al 0.35 Ga 0.65 As emitter and a base sheet resistance of 330 Ω/V exhibit very high DC current gain at all bias levels, with a DC current gain exceeding 140 @ 25 A/cm 2 and a peak DC current gain of 210 @ 26 kA/cm 2 . The temperature dependence of the peak DC current gain is significantly improved over a similar structure with a 25% AlGaAs emitter. The RF performance of the 35% AlGaAs structure is also comparable to the 25% structure, with an f t of 34 GHz and an f max of 55 GHz.
Role of Neutral Base Recombination in High Gain AlGaAs/GaAs HBT’s
Neutral base recombination is a limiting factor controlling the maximum gain of AlGaAs/GaAs HBT's with base sheet resistances between 100 and 350 = : In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600Å and the base doping level between 2.9 2 and 4.7 2 10 19 cm 03 : The dc current gain of large area devices (L = 75 m 2 75 m) varies by as much as a factor of two at high injection levels for a fixed base sheet resistance, depending on the growth optimization. One of these series (Series TA) has the highest current gains ever reported in this base sheet resistance range, with dc current gains over 225 (@ 200 A/cm 2 ) at a base sheet resistance of 330 = : A high dc current gain of 220 (@ 10 kA/cm 2 ) was also confirmed in small area devices (L = 8 m 28 m). High-frequency tests on a separate set of wafers grown under the same conditions indicate these high current gains can be achieved without compromising the RF characteristics: Both high and normal gain devices exhibit an ft 68 GHz and fmax 100 GHz. By fitting the base current as a sum of two components, one due to recombination in the neutral base and the other in the space charge region, we conclude that an improvement in the minority carrier lifetime is responsible for the observed increase in dc current gain. Moreover, we observe a thickness-dependent variation in the effective minority carrier lifetime as the gains increase, along with a nonlinear dependence of current gain on base doping. Both phenomena are discussed in terms of an increase in Auger and radiative recombination relative to Hall-Shockley-Read recombination in optimized samples.