High DC Current Gain Research Articles

Fabrication and Characterization of Self-Aligned InAlAs/InGaAsSb/InGaAs Double Heterojunction Bipolar Transistors

A trilevel resist system was employed to fabricate self-aligned, submicron emitter finger In0.52Al0.48As/In0.42Ga0.58As0.77Sb0.23/ In0.53Ga0.47As double heterojunction bipolar transistors (DHBTs). Selective wet-etchants were used to define the emitter fingers and to form an InGaAs guard-ring around the emitter fingers. Due to the low energy bandgap of the InGaAsSb base layer and type II base-collector junction, a low turn-on voltage of 0.38 V at 1 A/cm2 and a high dc current gain of 123.8 for a DHBT with a 0.65 x 8.65 µm2 emitter area were obtained. A unity gain cut-off frequency (fT) of 260 GHz and a maximum oscillation frequency (fmax) of 485 GHz at JC = 302 kA/cm2 were achieved.

Fabrication of InAlAs/InGaAsSb/InGaAs double heterojunction bipolar transistors

A trilevel resist system was employed to fabricate self-aligned, submicron emitter finger In0.52Al0.48As/In0.42Ga0.58As0.77Sb0.23/In0.53Ga0.47As double heterojunction bipolar transistors (DHBTs). Selective wet-etchants were used to define the emitter fingers and to form an InGaAs guard-ring around the emitter fingers. Due to the low energy bandgap of the InGaAsSb base layer and type II base-collector junction, a low turn-on voltage of 0.38 V at 1 A/cm2 and a high dc current gain of 123.8 for a DHBT with a 0.65×8.65 μm2 emitter area were obtained. A unity gain cutoff frequency (fT) of 260 GHz and a maximum oscillation frequency (fmax) of 485 GHz at JC=302 kA/cm2 were achieved.

1600 V, 5.1 mΩ●cm<sup>2</sup> 4H-SiC BJT with a High Current Gain of β=70

This paper reports a newly achieved best result on the common emitter current gain of 4H-SiC high power bipolar junction transistors (BJTs). A fabricated 1600 V – 15 A 4H-SiC power BJT with an active area of 1.7 mm2 shows a high DC current gain (b) of 70, when it conducts 9.8 A collector current at a base current of only 140 mA. The maximum AC current gain (DIC/DIB) is up to 78. This high performance BJT has an open base collector-to-emitter blocking voltage (VCEO) of over 1674 V with a leakage current of 1.6 μA, and a specific on-resistance (RSP-ON) of 5.1 mW.cm2 when it conducts 7.0 A (412 A/cm2) at a forward voltage drop of VCE = 2.1 V. A large area 4H-SiC BJT with a footprint of 4.1 mm x 4.1 mm has also shown a DC current gain over 50. These high-gain, high-voltage and high-current 4H-SiC BJTs further support a promising future for 4H-SiC BJT applications.

Influence of emitter-ledge thickness on the surface- recombination mechanism of InGaP/GaAs heterojunction bipolar transistor

Abstract In this work, the characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with various emitter-ledge thicknesses are comprehensively studied and demonstrated. Based on the two-dimensional analysis, some important parameters such as the recombination rate and DC characteristics are studied. The simulated analyses are in good agreement with experimental results. It is known that better HBT performance, including lower recombination rate in the surface channel, and higher DC current gain are obtained in the studied devices with the emitter ledge thickness between 100 and 200 A.

High-Gain Arsenic-Rich n-p-n InP/GaAsSb DHBTs With $F_{T} ≫ \hbox{420}\ \hbox{GHz}$

Type-II n-p-n InP/GaAsSb/InP double heterostructure bipolar transistors (DHBTs) that are fabricated by optical lithography with a 0.6 times 5 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter on a 20-nm compositionally uniform GaAsSb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> , carbon-doped base with x = 0.60 and a 75-nm InP collector show current-gain cutoff frequencies as high as 423 GHz at 10 mA/mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and feature a BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</sub> = 4 V. The pseudomorphic As-rich InP/GaAsSb DHBTs feature a high maximum dc current gain of > 160, owing to the reduction of the type-II conduction band discontinuity DeltaE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> and the associated recombination at the InP/GaAsSb emitter-base interface. This brief demonstrates that the InP/GaAsSb DHBT technology can combine high gain, wide bandwidths, high-current drivability, and structural simplicity.

1000-V, 30-A 4H-SiC BJTs with high current gain

This paper presents the development of 1000 V, 30A bipolar junction transistor (BJT) with high dc current gain in 4H-SiC. BJT devices with an active area of 3/spl times/3 mm/sup 2/ showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm/sup 2/, at a forward voltage drop of 2 V. A common-emitter current gain of 40, along with a low specific on-resistance of 6.0m/spl Omega//spl middot/cm/sup 2/ was observed at room temperature. These results show significant improvement over state-of-the-art. High temperature current-voltage characteristics were also performed on the large-area bipolar junction transistor device. A collector current of 10A is observed at V/sub CE/=2 V and I/sub B/=600 mA at 225/spl deg/C. The on-resistance increases to 22.5 m/spl Omega//spl middot/cm/sup 2/ at higher temperatures, while the dc current gain decreases to 30 at 275/spl deg/C. A sharp avalanche behavior was observed at a collector voltage of 1000 V. Inductive switching measurements at room temperature with a power supply voltage of 500 V show fast switching with a turn-off time of about 60 ns and a turn-on time of 32 ns, which is a result of the low resistance in the base.

ANALYSIS OF HIGH DC CURRENT GAIN STRUCTURES FOR GaN/InGaN/GaN HBTs

AlGaN/GaN HBTs with DC current gains in excess of 10 have been demonstrated; however, Makimoto et al have recently obtained a DC current gain value exceeding 2000 for a GaN/InGaN/GaN triple mesa DHBT.1,2,3 The experimental demonstration of a GaN -based HBT with such extraordinary DC current gain has motivated the search for new device structures conducive to high DC current gain. Simulations in this work indicate that high DC current gain is difficult to achieve with a uniform, defect-free base layer. We also simulate the electrical characteristics of a new class of DHBT where the base layer is non-uniform. By non-uniformly thinning or perforating the base, the majority of the base would remain thick to minimize the negative impact to base resistance. However, small thinned regions achieve extremely high DC current gain, which can be used to significantly increase the overall DC current gain. This device structure could naturally occur when "V" defects form or Indium is non-uniformly distributed during the base layer growth. The sensitivity of DC current gain to the base thickness range, duty cycle, defect geometry, and defect type is also investigated.

A High Voltage (1,750V) and High Current Gain (β=24.8) 4H-SiC Bipolar Junction Transistor using a Thin (12 μm) Drift layer

This paper reports the first, near theoretical limit breakdown voltage (1,750V) 4H-SiC BJTs with both high DC current gain(24.8) and low specific on-resistance (8.4m Ω·cm 2 at 50A/cm 2 and 12m Ω·cm 2 at 356A/cm 2 ) based on a drift layer of only 12 μm, doped to 8.5x10 15 cm -3 . The high performance is achieved through the use of an optimum single-step junction termination extension (JTE), Al-free base Ohmic contact and wet-oxygen low-temperature re-oxidation annealing. Detailed processing conditions are reported. Room temperature and high temperature current- voltage characteristics are also reported.

A 500V, Very High Current Gain (β=1517) 4H-SiC Bipolar Darlington Transistor

A 500V, Very High Current Gain (β=1517) 4H-SiC Bipolar Darlington Transistor

High voltage (&gt;1kV) and high current gain (32) 4H-SiC power BJTs using Al-free ohmic contact to the base

This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/.

Scaling of microwave noise and small-signal parameters of InP/InGaAs DHBT with high DC current gain

The scaling of noise and small-signal parameters of InP double heterojunction bipolar transistors (DHBTs) with high DC gain are presented for the first time in this brief. As InP DHBTs have very low surface recombination and high DC current gain, the large size device can be viewed as consisting of n identical subcells. Using this approach, a set of equations was derived, which relate the noise and small-signal parameters between the large-size device and the subcells for scaling purposes. The experimental and theoretical results show that at the same collector current density and collector-emitter voltage, good scaling of the noise and small-signal parameters can be achieved between the large-size device and the subcells. Because of the nonscalable external base-collector capacitor (C/sub bc/), the effects of C/sub bc/ on the noise and small-signal parameters are also investigated. The large base-collector capacitance acts as a negative feedback providing the lower minimum noise figure value and higher value of the imaginary part of the optimum source admittance. The good agreement between the measured and the calculated results supports the scaling approach developed in this work for InP DHBTs that may be useful for the design of high frequency circuits using InP-based HBTs.

Investigation of an InGaP/GaAs resonant-tunneling heterojunction bipolar transistor

An interesting InGaP/GaAs resonant-tunneling heterojunction bipolar transistor incorporating a superlattice (SL) structure in the emitter has been fabricated and studied. With the n-type doped well, the strongly coupling effect dominating the biased SL behaves like a double barrier operation. On the basis of the transfer matrix method, the transport mechanism of sequential miniband conduction can be developed by the theoretical calculation associated with the RT in the studied SL structure. Experimentally, the double negative differential resistance phenomena are presented both in the two-and three-terminal current–voltage characteristics at 300 K. In addition, excellent transistor behaviors including the high dc current gain as high as 70, low saturation voltage smaller than 1.2 V, low offset voltage of 110 mV and high breakdown voltage larger than 20 V are obtained.

Turn-on voltage investigation of GaAs-based bipolar transistors with Ga/sub 1-x/In/sub x/As/sub 1-y/Ny base layers

The fundamental lower limit on the turn on voltage of GaAs-based bipolar transistors is first established, then reduced with the use of a novel low energy-gap base material, Ga/sub 1-x/In/sub x/As/sub 1-y/N/sub y/. InGaP/GaInAsN DHBTs (x/spl sim/3y/spl sim/0.01) with high p-type doping levels (/spl sim/3/spl times/10/sup 19/ cm/sup -3/) and dc current gain (/spl beta//sub max//spl sim/68 at 234 /spl Omega///spl square/) are demonstrated. A reduction in the turn-on voltage over a wide range of practical base sheet resistance values (100 to 400 /spl Omega///spl square/) is established relative to both GaAs BJTs and conventional InGaP/GaAs HBTs with optimized base-emitter interfaces-over 25 mV in heavily doped, high dc current gain samples. The potential to engineer turn-on voltages comparable to Si- or InP-based bipolar devices on a GaAs platform is enabled by the use of lattice matched Ga/sub 1-x/In/sub x/As/sub 1-y/N/sub y/ alloys, which can simultaneously reduce the energy-gap and balance the lattice constant of the base layer when x/spl sim/3y.

High DC current gain InGaP/GaAs HBTs grown by LP-MOCVD

The high current gain of InGaP/GaAs heterojunction bipolar transistors (HBTs) grown under optimised growth conditions using MOCVD is demonstrated. Large area (60 µm × 60 µm) samples of InGaP/GaAs HBTs are grown and fabricated for DC characterisation. These devices show Gummel plots with nearly ideal I-V characteristics (nc = 1.00 and nb = 1.09). Measured current gain of the devices with a base sheet resistance Rb of 236 Ω/sq is 130 at a collector current Ic of 1 mA and 147 at the collector current density of 1 kA/cm2 (Ic = 39.1 mA). The current gain to base sheet resistance ratio is 0.623 at 1 kA/cm2, which is the highest value ever reported. The optimised growth condition improves the current gain in the entire range of the collector current. The current gain is as high as 92 at an Ic of 10 µA. These results are the best that have ever been demonstrated with InGaP/GaAs HBTs. The data show that the MOCVD growth condition is an important factor in achieving high current gain in InGaP/GaAs HBTs.

GaN/SiC heterojunction bipolar transistors

We report on the evolution of the fabrication and characterization of high-temperature and high-power GaN/SiC n–p–n heterojunction bipolar transistors (HBTs). The HBT structures consists of an n-type GaN emitter and a SiC p–n base/collector. Initially, the HBTs were fabricated using reactive ion etching (RIE) to define both the emitter and base areas. However, the poor etch selectivity between GaN and SiC made it difficult to stop at the thin base layer. Furthermore, the RIE caused damage at the heterojunctions, which resulted in large leakage currents. Selective area growth was therefore employed to form the n-GaN emitters. GaN/SiC HBTs were first demonstrated using the 6H-polytype. These transistors had an extraordinary high dc current gain of >10 6 at room temperature and were able to operate at 520°C with a current gain of 100. However, in more recent work, this performance could not easily be reproduced due to the presence of a parasitic deep defect level in the p-type 6H–SiC. The possibility of obtaining higher quality 4H–SiC than 6H–SiC, without this defect level, seemed promising since much of the materials development is focused on 4H–SiC, due to its larger energy band gap and superior electron mobility. GaN/4H–SiC HBTs are demonstrated with a modest dc current gain of 15 at room temperature and 3 at 300°C.

High performance Al/sub 0.35/Ga/sub 0.65/As/GaAs HBT's

AlGaAs emitter heterojunction bipolar transistors (HBTs) are demonstrated to have excellent dc and RF properties comparable to InGaP/GaAs HBTs by increasing the Al composition. Al/sub 0.35/Ga/sub 0.65/As/GaAs HBTs exhibit very high dc current gain at all bias levels, exceeding 140 at 25 A/cm/sup 2/ and reaching a maximum of 210 at 26 kA/cm/sup 2/ (L=1.4 /spl mu/m/spl times/3 /spl mu/m, R/sub sb/=330 /spl Omega///spl square/). 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.

A comparative study of GaAs- and InP-based HBT growth by means of LP-MOVPE using conventional and non gaseous sources

Low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) growth of carbon doped (InGa)P/GaAs and InP/(InGa)As heterojunction bipolar transistors (HBT) is presented using a non-gaseous source (ngs-) process. Liquid precursors TBAs/TBP for the group-V and DitBuSi/CBr 4 for the group-IV dopant sources are compared to the conventional hydrides AsH 3/PH 3 and dopant sources Si 2H 6/CCl 4 while using TMIn/TEGa in both cases. The thermal decomposition of the non gaseous sources fits much better to the need of low temperature growth for the application of carbon doped HBT. The doping behavior using DitBuSi/CBr 4 is studied by van der Pauw Hall measurements and will be compared to the results using Si 2H 6/CCl 4. Detailed high resolution X-ray diffraction (HRXRD) analysis based on 004 and 002 reflection measurements supported by simulations using BEDE RADS simulator enable a non-destructive layer stack characterization. InGaP/GaAs HBT structures designed for rf-applications are grown at a constant growth temperature of T gr=600°C and at a constant V/III-ratio of 10 for all GaAs layers. P-type carbon concentrations up to p = 5·10 19cm −3 and n-type doping concentrations up to n = 7·10 18cm −3 are achieved. The non self-aligned devices (A E = 3·10 μm 2)_show excellent performance, like a dc-current gain of B max = 80, a turn on voltage of V offset = 110 mV (Breakdown Voltage V CEBr,0 > 10 V), and radio frequency properties of f T/f max = 65 GHz/59 GHz. In the non-gaseous source configuration the strong reduction in the differences of V/III-ratios and temperatures during HBT structure growth enable easier LP-MOVPE process control. This is also found for the growth InP/InGaAs HBT where a high dc-current gain and high transit frequency of f T= 120 GHz are achieved.

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 /spl Omega///spl square/. In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600 /spl Aring/ and the base doping level between 2.9/spl times/ and 4.7/spl times/10/sup 19/ cm/sup -3/. The dc current gain of large area devices (L=75 /spl mu/m/spl times/75 /spl mu/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/sup 2/) at a base sheet resistance of 330 /spl Omega///spl square/. A high dc current gain of 220 (@ 10 kA/cm/sup 2/) was also confirmed in small area devices (L=8 /spl mu/m/spl times/8 /spl mu/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 f/sub t//spl sim/68 GHz and f/sub max//spl sim/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.

High-gain, high-speed InP/InGaAs double-heterojunction bipolar transistors with a step-graded base-collector heterojunction

We show that by using InP for the emitter and collector layers, and a thin high-doped base layer, it is possible to achieve both a high DC current gain and a high maximum frequency of oscillation. We have fabricated InP/InGaAs double heterojunction bipolar transistors (DHBT's) with cutoff frequencies f/sub T/ and f/sub max/ of 92 and 95 GHz, respectively, with a DC current gain of over 100. The maximum cutoff frequencies were 107 and 104 GHz. >

High-performance microwave AlGaAs-InGaAs Pnp HBT with high-DC current gain

An Pnp heterojunction bipolar transistor (HBT) which had among the highest reported values of f/sub T/( approximately 23 GHz) and f/sub max/( approximately 40 GHz) employed a heavily doped InGaAs pseudomorphic base. However, this HBT had very low values of DC current gain (<or=4). Pnp microwave HBTs with a modified base design are reported. These HBTs not only achieve similar high-frequency performance, but also attain dramatically higher current gain values approximately 90.<<ETX>>