Submicron-square emitter AlGaAs/GaAs HBTs with AlGaAshetero-guardring

Successful operation of submicron-square emitter AlGaAs/GaAs HBTs is demonstrated for the first time by using a fully mesa-structure-type emitter-base junction-area definition method with an AlGaAs hetero-guardring. The hetero-guardring reduces surface recombination current at the emitter-mesa edge to 1.4 μA/μm. This is 1/10 of that for devices without the guardring. Here, dc gains of 20, 26, and 40 are achieved for 0.5 μm×0.5 μm, 0.7 μm×0.7 μm, and 0.9 μm×0.9 μm emitter HBTs, respectively. An f_T of 40 GHz, and an f_max of 30 GHz are obtained for 0.9 μm×0.9 μm at a J_C of 1.0×10⁵ A/cm²     

Design study of AlGaAs/GaAs HBTs

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 S_E<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     

GaAs/AlGaAs heterojunction Pnp bipolar transistors grownon (100) Si by molecular beam epitaxy

GaAs/AlGaAs Pnp heterojunction bipolar transistors (HBTs) were fabricated and tested on (100) Si substrates for the first time. A common-emitter current gain of β=8 was measured for the typical devices with an emitter area of 50×50 μm² at a collector current density of 1×10⁴ A/cm² with no output negative differential resistance up to 280 mA, highest current used. A very high base-collector breakdown voltage of 10 V was obtained. Comparing the similar structures grown on GaAs substrates, the measured characteristics clearly demonstrate that device grade hole injection can be obtained in GaAs on Si epitaxial layers despite the presence of dislocations     

Submicrometer self-aligned AlGaAs/GaAs heterojunction bipolartransistor process suitable for digital applications

A self-aligned process is developed to obtain submicrometer high-performance AlGaAs/GaAs heterojunction bipolar transistors (HBTs) which can maintain a high current gain for emitter sizes on the order of 1 μm². The major features of the process are incorporation of an AlGaAs surface passivation structure around the entire emitter-base junction periphery to reduce surface recombination and reliable removal of base metal (Ti/W) deposits from the sidewall by electron cyclotron resonance (ECR) plasma deposition of oxide and ECR plasma etching by NF₃. A DC current gain of more than 30 can be obtained for HBTs with an emitter-base junction area of 0.5×2 μm² at submilliampere collector currents. The maximum f_T and f_max obtained from a 0.5×2 μm² emitter HBT are 46 and 42 GHz, respectively at I_C=1.5 and more than 20 GHz even at I_C=0.1 mA     

Uniform, high-gain AlGaAs/In0.05Ga0.95As/GaAsP-n-p heterojunction bipolar transistors by dual selective etch process

AlGaAs/InGaAs/GaAs P-n-p heterojunction bipolar transistors (HBTs) have been fabricated using a dual selective etch process. In this process, a thin AlGaAs surface passivation layer surrounding the emitter is defined by selective etching of the GaAs cap layer. The InGaAs base is then exposed by selective etching of the AlGaAs emitter. The resulting devices were very uniform, with current gain varying by less than ±10% for a given device size. Current gain at a given emitter current density was independent of device size, with gains of over 200 obtained at current densities above 5×10⁴ A/cm ²     

Electron irradiation effects in AlGaAs/GaAs single heterojunctionbipolar transistors

The effects of high-energy electron irradiation on the dc characteristics of polyimide passivated AlGaAs/GaAs HBTs of different base thicknesses and different emitter sizes are investigated. The devices show gain degradation for doses greater than 10¹⁵ e/cm². The gain degradation of the passivated devices decreases (1) with increase in the base thickness, (2) with increase in the perimeter to area ratio of the emitter, and (3) with increase in the base current. Our results suggest that the observed gain degradation due to electron irradiation is mainly caused by an increase in the emitter-base junction space charge region recombination     

High reliability InGaP/GaAs HBT

Excellent long term reliability InGaP/GaAs heterojunction bipolar transistors (HBT) grown by metalorganic chemical vapor deposition (MOCVD) are demonstrated. There were no device failures (T=10000 h) in a sample lot of ten devices (L=6.4 μm ×20 μm) under moderate current densities and high-temperature testing (J_c=25 kA/cm ², V_ce=2.0 V, Junction Temp =264°C). The dc current gain for large area devices (L=75 μm ×75 μm) at 1 kA/cm² at a base sheet resistance of 240 ohms/sq (4×10 ¹⁹ cm^-3@700 Å) was over 100. The dc current gain before reliability testing (L=6.4 μm ×10 μm) at 0.8 kA/cm² was 62. The dc current gain (0.8 kA/cm²) decreased to 57 after 10000 h of reliability testing. The devices showed an f_T=61 GHz and f_max=103 GHz. The reliability results are the highest ever achieved for InGaP/GaAs HBT and these results indicate the great potential of InGaP/GaAs HBT for numerous low- and high-frequency microwave circuit applications. The reliability improvements are probably due to the initial low base current at low current densities which result from the low surface recombination of InGaP and the high valence band discontinuity between InGaP and GaAs     

Stress current behavior of InAlAs/InGaAs and AlGaAs/GaAs HBT's withpolyimide passivation

InAlAs/InGaAs and AlGaAs/GaAs HBTs, with heavily Be-doped base layers, have been fabricated and their reliability under excessive forward current tested. To understand the HBT material difference, a common process based on a polyimide planarization method is applied to the fabrication. While short-term degradation induced by stress current is observed for AlGaAs/GaAs HBTs, InAlAs/InGaAs HBTs are stable up to a current density of 1.5×10⁵ A/cm², indicating the absence of substantial Be diffusion. An analysis of base current has shown a striking contrast between the HBTs in terms of the stressing effect on the surface recombination along emitter junction periphery     

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 Ω/□. In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600 Å and the base doping level between 2.9× and 4.7×10¹⁹ cm^-3. The dc current gain of large area devices (L=75 μm×75 μm) 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/cm² ) at a base sheet resistance of 330 Ω/□. A high dc current gain of 220 (@ 10 kA/cm²) was also confirmed in small area devices (L=8 μm×8 μm). 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_t ~68 GHz and f_max~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     

Metamorphic InP/InGaAs heterojunction bipolar transistors on GaAssubstrate: DC and microwave performances

High-performance InP/In_0.53Ga_0.47As metamorphic heterojunction bipolar transistors (MHBTs) on GaAs substrate have been fabricated using In_xGa_1-xP strain relief buffer layer grown by solid-source molecular beam epitaxy (SSMBE). The MHBTs exhibited a dc current gain over 100, a unity current gain cutoff frequency (f_T) of 48 GHz and a maximum oscillation frequency (f_MAX) of 42 GHz with low junction leakage current and high breakdown voltages. It has also been shown that the MHBTs have achieved a minimum noise figure of 2 dB at 2 GHz (devices with 5×5 μm ² emitter) and a maximum output power of 18 dBm at 2.5 GHz (devices with 5×20 μm² emitter), which are comparable to the values reported on the lattice-matched HBTs (LHBTs). The dc and microwave characteristics show the great potential of the InP/InGaAs MHBTs on GaAs substrate for high-frequency and high-speed applications     

Fully-planar AlGaAs/GaAs HBT's achieved by selective CBE regrowth

This paper describes a novel fully planar AlGaAs/GaAs heterojunction bipolar transistor (HBT) technology using selective chemical beam epitaxy (CBE). Planarization is achieved by a selective regrowth of the base and collector contact layers. This process allows the simultaneous metallization of the emitter, base and collector on top of the device. For the devices with an emitter-base junction area of 2×6 μm² and a base-collector junction area of 14×6 μm², a current gain cut off frequency of 50 GHz and a maximum oscillation frequency of 30 GHz are achieved. The common emitter current gain h_FE is 25 for a collector current density J_c of 2×10⁴ A/cm²     

Self-aligned InGaP/GaAs heterojunction bipolar transistors formicrowave power application

As an alternative to AlGaAs/GaAs heterojunction bipolar transistors (HBTs) for microwave applications, InGaP/GaAs HBTs with carbon-doped base layers grown by metal organic molecular beam epitaxy (MOMBE) with excellent DC, RF, and microwave performance are demonstrated. As previously reported, with a 700-Å-thick base layer (135-Ω/sq sheet resistance), a DC current gain of 25, and cutoff frequency and maximum frequency of oscillation above 70 GHz were measured for a 2-μm×5-μm emitter area device. A device with 12 cells, each consisting of a 2-μm×15-μm emitter area device for a total emitter area of 360 μm², was power tested at 4 GHz under continuous-wave (CW) bias condition. The device delivered 0.6-W output power with 13-dB linear gain and a power-added efficiency of 50%     

A high-gain GaAs/AlGaAs n-p-n heterojunction bipolar transistor on(100) Si grown by molecular beam epitaxy

High-gain GaAs/AlGaAs n-p-n heterojunction bipolar transistors (HBT's) on Si substrates grown by molecular beam epitaxy (MBE) have been fabricated and tested. In this structure, an n⁺-InAs emitter cap layer was grown in order to achieve a nonalloyed ohmic contact. Typical devices with an emitter dimension of 50×50 μm² exhibited a current gain as high as 45 at a collector current density of 2×10³ A/cm² with an ideality factor of 1.4. This is the highest current gain reported for HBT's grown on Si substrates. Breakdown voltages as high as 10 and 15 V were observed for the emitter-base and collector-base junctions respectively. The investigation on devices with varying emitter dimensions demonstrates that much higher current gains can be expected     

Extrinsic base surface passivation in GaInP/GaAs heterojunctionbipolar transistors

The authors demonstrate excellent passivation of the extrinsic base surfaces in GaInP/GaAs heterojunction bipolar transistors (HBTs) having small emitter areas. Passivated devices with an area as small as 4×20 μm² exhibit the highest reported current gain value of 2690 for GaInP/GaAs HBTs, while unpassivated 4×20-μm ² devices exhibit a current gain of only 500. Measured current gains as a function of collector current density are almost identical for devices with varying emitter widths of 4, 6, 8, 12, 16, and 100 μm. The current gains are also nearly identical for devices with varying passivation ledge widths of 1, 2, 3, and 6 μm. These results are contrasted with those of a previously published study reporting surface passivation for a GaInP/GaAs HBT with a large emitter area     

AlGaAs/Ge/GaAs heterojunction bipolar transistors grown bymolecular beam epitaxy

An N-Al_0.22Ga_0.78As emitter, p-Ge base, and n-GaAs collector (AlGaAs/Ge/GaAs) heterojunction bipolar transistor (HBT) in the emitter-up configuration grown by molecular beam epitaxy is discussed. Devices exhibited common-emitter current gains of as high as 300 at a collector current density of 2000 A/cm² and a collector voltage of 4 V. As the device area is reduced from 50×50 to 10×40 μm, the current gain did not show significant changes, suggesting a low surface recombination velocity in the Ge base     

Growth and metallization of AlGaAs/GaAs carbon-doped HBTs usingtrimethylamine alane by CBE

It is shown that the entire structure of high-quality AlGaAs/GaAs heterojunction bipolar transistors (HBTs) including a nonalloyed δ-doped ohmic contact and in-situ Al metallization can be grown by chemical beam epitaxy (CBE) using a new precursor, trimethylamine alane, as the Al source. The graded Al_xGa_1-xAs and uniform GaAs bases (both ~1000 A thick) are doped with carbon to high 10 ¹⁹ cm^-3 using trimethyl-Ga. A current gain of 10 at a current density of 2500 A/cm² is obtained for both uniform- and graded-base HBTs. Both devices show good output characteristics     

Influence of dislocations on the DC characteristics of AlGaAs/GaAsheterojunction bipolar transistors

The influence of dislocations on the minority electron lifetime in p-type GaAs layers and on AlGaAs/GaAs HBTs has been investigated. The minority electron lifetime in 1×10¹⁹/cm³ doped p-GaAs decreases significantly when the dislocation density is greater than 10⁷/cm². This result agrees well with analysis of carrier transport in highly dislocated material. Current gain reduction in HBTs with high dislocation density is found to be due to two effects: reduction of the electron lifetime in the base layer and an increase of the recombination current in the emitter-base junction depletion region. These two effects are comparable in reducing the current gain     

Small-scaled InGaP/GaAs HBTs with WSi/Ti base electrode and buriedSiO2

This paper describes the fabrication and characteristics of small-scaled InGaP/GaAs HBTs with high-speed as well as low-current operation. To reduce both the emitter size S_E and the base-collector capacitance C_BC simultaneously, the HBTs are fabricated by using WSi/Ti as the base electrode and by burying SiO₂ in the extrinsic base-collector region under the base electrode. WSi/Ti simplifies and facilitates processing to fabricate a small base electrode, and makes it possible to reduce the width of the base contact to less than 0.4 μm without the large increase in the base resistance. The DC current gain of 20 is obtained for an HBT with S _E of 0.3×1.6 μm² due to the suppression of emitter size effect by using InGaP as the emitter material. An HBT with SE of 0.6×4.6 μm² exhibited f_T of 138 GHz and f_max of 275 GHz at I_C of 4 mA; and an HBT with SE of 0.3×1.6 μm² exhibited f_T of 96 GHz and f_max of 197 GHz at I_C of 1 mA. These results indicate the great potential of these HBTs for high-speed and low-power circuit applications     

Microwave performance of a self-aligned GaInP/GaAs heterojunctionbipolar transistor

The microwave performance of a self-aligned GaInP/GaAs heterojunction bipolar transistor (HBT) is presented. At an operating current density of 2.08×10⁴ A/cm², the measured cutoff frequency is 50 GHz and the maximum oscillation frequency extrapolated from measured unilateral gain and the maximum available gain are 116 and 81 GHz, respectively, all using 20-dB/decade slopes. These results are compared with other reported high-frequency performances of GaInP HBTs. In addition, these results are compared with AlGaAs/GaAs HBTs having a similar device structure     

Monolithically integrated SQW laser and HBT laser driver viaselective OMVPE regrowth

An AlGaAs/GaAs nan heterojunction bipolar transistor (HBT) laser driver circuit and a pseudomorphic InGaAs/GaAs/AlGaAs graded index single-quantum-well (SQW) laser have been laterally integrated to maintain surface planarity using selective organometallic vapor-phase epitaxy (OMVPE) regrowth of the HBT. The self-aligned HBTs exhibit a DC current gain of 30 and an f_t (f_max ) of 45(60) GHz. The 980-nm lasers exhibit room-temperature threshold current densities as low as 420(320) A/cm² for CW (pulsed) operation. The cavities are 40(7) μm×500 μm and have less than 1(2) Ω of series resistance. SPICE simulations of the integrated driver indicate that operating speeds of over 10 Gb/s are possible