Role of Neutral Base Recombination in High Gain AlGaAs/GaAs HBT’s (original) (raw)
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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.
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.
Design study of AlGaAs/GaAs HBTs
IEEE Transactions on Electron Devices, 1990
The frequency performance of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) having different layouts, doping profiles, and layer thicknesses was assessed using the BIPOLE computer program. The optimized design of HBTs was studied, and the high current performances of HBTs and polysilicon emitter transistors were compared. It is shown that no current crowding effect occurs at current densities less than 1×105 A/cm2 for the HBT with emitter stripe width SE<3 μm, and the HBT current-handling capability determined by the peak current-gain cutoff frequency is more than twice as large as that of the polysilicon emitter transistor. An optimized maximum oscillation frequency formula has been obtained for a typical process n-p-n AlGaAs/GaAs HBT having base doping of 1×10 19 cm-3
An AlGaAs double-heterojunction bipolar transistor grown by molecular-beam epitaxy
Applied Physics Letters, 1991
To study AlGaAs p-n heterojunctions and optical and transport properties of electrically injected minority carriers (electrons) in p-A1,,,Gac,5 As, we have tested the performance of Ab,,Gao,4As/Alo.25Ga,,~ As/Ale6Gac.,As NpN double-heterojunction bipolar transistors ( DHBTs). The transistors exhibited a common emitter current gain (fi) as high as 400 at a current density of 2 kA cm -2. From the Gummel plots, the ideality factors (n) of emitter-base and base-collector junctions were as low as 1.37 and 1.01, respectively, indicating high quality of both the junctions. Assuming a unity current injection efficiency, we obtain an electron diffusion length of 1.2 pm for an acceptor density of 6.0~ lOI cm -3 in p-Alc25Gac75A~. Due to the wide band-gap materials, the device has the potential for useful operation at very high temperatures. The device also works as a bright red light emitter when the emitter-base junction is forward biased and the collector is either floating or forward biased, indicating dominance of radiative recombination in the base. Furthermore, the device also works as a phototransistor for detection of short wavelengths ( < 7 10 nm) with no sensitivity to longer wavelengths.
High-speed small-scale InGaP/GaAs HBT technology and its application to integrated circuits
IEEE Transactions on Electron Devices, 2001
We have developed the advanced performance, smallscale InGaP/GaAs heterojunction bipolar transistors (HBTs) by using WSi/Ti base electrode and buried SiO 2 in the extrinsic collector. The base-collector capacitance BC was further reduced to improve high-frequency performance. Improving the uniformity of the buried SiO 2 , reducing the area of the base electrode, and optimizing the width of the base-contact enabled us to reduce the parasitic capacitance in the buried SiO 2 region by 50% compared to our previous devices. The cutoff frequency T of 156 GHz and the maximum oscillation frequency max of 255 GHz were obtained at a collector current C of 3.5 mA for the HBT with an emitter size E of 0.5 4.5 m 2 , and T of 114 GHz and max of 230 GHz were obtained at C of 0.9 mA for the HBT with E of 0.25 1.5 m 2 . We have also fabricated digital and analog circuits using these HBTs. A 1/8 static frequency divider operated at a maximum toggle frequency of 39.5 GHz with a power consumption per flip-flop of 190 mW. A transimpedance amplifier provides a gain of 46.5 dB with a bandwidth of 41.6 GHz at a power consumption of 150 mW. These results indicate the great potential of our HBTs for high-speed, low-power circuit applications.
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.
Metalorganic chemical vapor deposition of AlGaAs and InGaP heterojunction bipolar transistors
Journal of Crystal Growth, 2001
Heterojunction bipolar transistors (HBT) are now beginning to be widely incorporated as power amplifiers, laser drivers, multiplexers, clock data recovery circuits, as well as transimpedance and broadband amplifiers in high performance millimeter wave circuits (MMICs). The increasing acceptance of this device is principally due to advancements in metalorganic chemical vapor deposition (MOCVD), device processing, and circuit design technologies. Many of the DC electrical characteristics of large area devices can be directly correlated to the DC performance of small area RF devices. A precise understanding of the growth parameters and their relationship to device characteristics is critical for ensuring the high degree of reproducibility required for low cost high-yield volume manufacturing. Significant improvements in the understanding of the MOCVD growth process have been realized through the implementation of statistical process control on the key HBT device parameters. This tool has been successfully used to maintain the high quality of the device characteristics in high-volume production of 4 00 GaAs-based HBTs. There is a growing demand to migrate towards 6 00 diameter wafer size due to the potential cost reductions and increased volume production that can be realized. Preliminary results, indicating good heterostructure layer characteristics, demonstrate the feasibility of 6 00 InGaPbased HBT devices.
Solid State Communications, 2006
In this work we investigate the optical and band structure properties of full InGaP/GaAs based heterojunction bipolar transistor (HBT) epitaxial structures grown by metalorganic chemical vapour phase epitaxy (MOVPE). In related work, full HBTs have been fabricated from the two wafers studied, which exhibit high and low common-emitter current gain (h FE ) parameters on electrical test. The focus of this study is to investigate and compare the photoluminescence and photore¯ectance spectroscopy response of these known good and bad epitaxial wafers. The results of low temperature (10±300 K) spectral and transient photoluminescence (PL) analysis are presented, revealing evidence of the nature of the InGaP ordering induced non-radiative loss mechanism. The results also demonstrate the modi®cation to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental results are supported by X-ray diffraction data and ®nite-element device simulation, showing the effect of intermixing layers on the interfacial band potentials. The optical modulation technique of photo-re¯ectance (PR) spectroscopy was employed to investigate the band structure and interfacial electric ®elds, F s , of the HBT structures. Following the polarisation±[110] and [11 Å 0]±dependence of the sub-lattice ordering PR response, it was found necessary to include an emitter/ base intermixing layer in order to account for the InGaP/GaAs F s data. It is concluded that non-optimal MOVPE growth conditions for one of the structures resulted in both sub-lattice ordering and layer intermixing effects, consistent with the low h FE of the HBTs fabricated from this material. q
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.
Structure and carrier lifetime in LT-GaAs
Journal of Electronic Materials, 1993
The relationship between the structural quality of low-temperature GaAs layers and the photoexcited carrier lifetime has been studied. Transmission electron microscopy, x-ray rocking curves, time-resolved reflectance methods, and photoconductive-switch-response measurements were used for this study. For a variety of samples grown at temperatures in the vicinity of200~ subpicosecond carrier lifetimes were observed both in as-grown layers, as well as in the same layers after post-annealing and formation of As precipitates. These results suggest that the carrier lifetime, which was found to be shorter in the as-grown layers than in the annealed ones, might be related to the density ofAsca antisite defects present in the layers. The annealed layers which contained structural defects before annealing appeared to exhibit the longest carrier lifetime due to gettering of As on these defects (and formation of relatively large As precipitates) and depletion of extra As (ASGa) defects from the layer. It was found as well that the responsivity of detectors fabricated on these layers depended strongly on the structural quality of the layers, with the greatest response obtained not for the layers with the fewest defects, but for the layers with 107-108/cm 2 of pyramidal defects.