Hot-electron InGaAs/InP heterostructure bipolar transistors withfT of 110 GHz

A hot-electron InGaAs/InP heterostructure bipolar transistor (HBT) is discussed. A unity-current-gain cutoff frequency of 110 GHz and a maximum frequency of oscillation of 58 GHz are realized in transistors with 3.2×3.2-μm² emitter size. Nonequilibrium electron transport, with an average electron velocity approaching 4×10⁷ cm/s through the thin (650 Å) heavily doped (p=5×10¹⁹ cm^-3) InGaAs base and 3000-Å-wide collector space-charge region, results in a transit delay of 0.5 ps corresponding to an intrinsic cutoff frequency of 318 GHz     

MBE-grown Si/SiGe HBTs with high β, fT,and fmax

Si/SiGe heterojunction bipolar transistors (HBTs) were fabricated by growing the complete layer structure with molecular beam epitaxy (MBE). The typical base doping of 2×10¹⁹ cm^-3 largely exceeded the emitter impurity level and led to sheet resistances of about 1 kΩ/□. The devices exhibited a 500-V Early voltage and a maximum room-temperature current gain of 550, rising to 13000 at 77 K. Devices built on buried-layer substrates had an f_max of 40 GHz. The transit frequency reached 42 GHz     

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     

Molecular beam epitaxial GaAs/AlGaAs heterojunction bipolartransistors on (311)A GaAs substrates with all-silicon doping

The authors have investigated the characteristics and reproducibility of Si-doped p-type (311)A GaAs layers for application to heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE). The authors obtained p=2.2×10¹⁹ cm^-3 in a layer grown at 670°C. They have used all-Si doping to grow n-p-n transistors. These devices exhibit excellent DC characteristics with β=230 in a device with base doping of p=4×10¹⁸ cm^-3     

Minority-carrier transport parameters in n-type silicon

Minority-carrier diffusion length L, lifetime τ, and diffusion coefficient D in n-type Si are measured at 296 K in the doping range from 10¹⁸ cm^-3 to 7×10¹⁹ cm^-3. The measurement is based on a lateral collection of carriers generated by a spatially uniform light. The distance between the illumination edge and the collection junction is defined by photolithography. This allows simultaneous and independent determination of all transport parameters in the same material. A self-consistency and accuracy check is provided by the relation L ²=Dτ. Details of experimental procedures are described. Empirical best-fit relations for the three parameters are given. The extraction of lifetime and diffusion coefficient was done in the frequency domain, which allows for straightforward elimination of parasitic effects in the nanosecond and subnanosecond range     

Minority-carrier transport parameters in degenerate n-type silicon

Direct measurements of the minority-hole transport parameters in degenerate n-type silicon were done by analyzing transient photocurrent in the frequency domain. Minority-hole mobility is found to increase with doping for dopings larger than 4×10¹⁹ cm^-3 . The ratio of minority-hole to majority-hole mobility is found to be about 2.8 at N_D=7.2×10¹⁹ cm^-3. The measured lifetime shows a strongly Auger-dependent mechanism. The extracted Auger coefficient at 296 K is C_n =2.22×10^-31 cm⁶-s^-1, and is in agreement with that reported on other works. Self-consistent checking is used to validate the accuracy of the measured results     

Frequency control of self-sustained pulsating laser diodes byuniform impurity doping into multiple-quantum-well structures

The self-sustained pulsating frequency in index guided AlGaAs multiple-quantum-well (MQW) laser diodes is controlled by impurity doping into the active region to reduce the relative intensity noise induced by optical feedback through a short optical path. Uniform n-type impurity doping into an MQW structure more effectively reduces the frequency by decreasing the differential gain than does modulation doping with an n-type impurity. Uniform doping of 1×10¹⁸ cm^-3 into each quantum well layer reduces the frequency to less than 0.8 GHz, which corresponds to half or two-thirds that of undoped lasers. The uniformly n-doped self-sustained pulsating lasers provided low noise characteristics with a relative intensity noise below 1×10³ Hz^-1 under an optical feedback of 20% even with a short optical path length of 60 mm     

⟨110⟩-oriented GaAs MESFETs

GaAs metal semiconductor field-effect transistors (MESFETs) have been successfully fabricated on molecular-beam epitaxial (MBE) films grown on the off-axis (110) GaAs substrate. The (110) substrates were tilted 6° toward the (111) Ga face in order to produce device quality two-dimensional MBE growth. Following the growth of a 0.4-μm undoped GaAs buffer, a 0.18-μm GaAs channel with a doping density of 3.4×10¹⁷ cm^-3 and a 0.12-μm contact layer with a doping density of 2×10¹⁸ cm^-3, both doped with Si, were grown. MESFET devices fabricated on this material show very low-gate leakage current, low output conductance, and an extrinsic transconductance of 200 mS/mm. A unity-current-gain cutoff frequency of 23 GHz and a maximum frequency of oscillation of 56 GHz have been achieved. These (110) GaAs MESFETs have demonstrated their potential for high-speed digital circuits as well as microwave power FET applications     

High-speed, high-current-gain p-n-p InP/InGaAs heterojunctionbipolar transistors

p-n-p InP/InGaAs heterojunction bipolar transistors (HBTs) are reported for the first time. The transistors, grown by metal organic molecular beam epitaxy (MOMBE), exhibited maximum DC current gain values up to 420 for a base doping level of 4×10¹⁸ cm^-3 . Small-signal measurements on self-aligned transistors with 3-μm×8-μm emitter area indicated the unity gain cutoff frequency value of 10.5 GHz and the inferred maximum frequency of oscillation of 25 GHz. The results clearly demonstrate the feasibility of complementary integrated circuits in the InP material system     

Drift hole mobility in strained and unstrained doped Si1-xGex alloys

Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 10¹⁵-10¹⁹ cm^-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×10¹⁹ cm^-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon     

Application of selective epitaxial silicon and chemo-mechanicalpolishing to bipolar transistors

Successful demonstration of single-polysilicon bipolar transistors fabricated using selective epitaxial growth (SEG) and chemo-mechanical polishing (CMP) is reported. The pedestal structure made possible by the SEG/CMP process combination results in significantly reduced extrinsic-base collector capacitance. Cut-off frequency (f_T) of devices with emitter stripe width of 1 μm, a base width of 110 nm, and a peak base doping of 3×10¹⁸ cm^-3 have been observed to improve from 16 GHz to 22 GHz when the extrinsic-base collector overlap is decreased from 1 μm to 0.2 μm. Leakage current, often a problem for SEG structures, has been reduced to 27 nA/cm² for the area component, and 10 nA/cm for the edge component, by (1) appropriate post-polish processing, including a high-temperature anneal and sacrificial oxidation, (2) aligning the device sidewalls along the 〈100〉 direction, and (3) the presence of the pedestal structure. Base-emitter junction nonideality in these transistors has also been investigated     

Modeling of currents in a vertical p-n-p transistor with extremelyshallow emitter

Detailed simulations of the collector current in a vertical poly-emitter p-n-p transistor have been carried out to verify the minority-hole mobility model of S.E. Swirhun et al. (ibid., vol.7, no.3, p.168-71, 1986). The simulations were based on the SIMS profile, incorporating all published physical parameters, and the results showed good agreement with the measurements for base doping ranging from 10¹⁸ to 10¹⁹ cm^-3. In addition, the effective surface recombination velocity of electrons at the p⁺ poly/Si interface was found by fitting the measured base current to be ~1.4×10⁵ cm/s, which is comparable to its n-p-n counterpart     

Effects of neutral buried p-layer on high-frequency performance ofGaAs MESFETs

Fully ion-implanted n⁺ self-aligned GaAs MESFETs with Au/WSiN refractory metal gates have been fabricated by adopting neutral buried p-layers formed by 50-keV Be-implantation. S-parameter measurements and equivalent circuit fittings are discussed. When the Be dose is increased from 2×10¹² cm^-2 to 4×10¹² cm^-2, the maximum value of the cutoff frequency with a 0.2-μm gate falls off from 108 to 78 GHz. This is because a neutral buried player makes the intrinsic gate-source capacitance increase markedly, while its influence on gate-drain capacitance and gate-source fringing capacitance is negligible. The maximum oscillation frequency recovers, however, due primarily to the drain conductance suppression by the higher-concentration buried p-layer. An equivalent value of over 130 GHz has been obtained for both 0.2-μm-gate GaAs MESFETs     

Reliability of AlInAs/GaInAs heterojunction bipolar transistors

The reliability of high-performance AlInAs/GaInAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE) is discussed. Devices with a base Be doping level of 5×10¹⁹ cm^-3 and a base thickness of approximately 50 nm displayed no sign of Be diffusion under applied bias. Excellent stability in DC current gain, device turn-on voltage, and base-emitter junction characteristics was observed. Accelerated life-test experiments were performed under an applied constant collector current density of 7×10⁴ A/cm² at ambient temperatures of 193, 208, and 328°C. Junction temperature and device thermal resistance were determined experimentally. Degradation of the base-collector junction was used as failure criterion to project a mean time to failure in excess of 10⁷ h at 125°C junction temperature with an associated activation energy of 1.92 eV     

Ultrahigh fT and fmax new self-alignmentInP/InGaAs HBT's with a highly Be-doped base layer grown by ALE/MOCVD

We report on a new self-alignment (SA) process and microwave performance of ALE/MOCVD grown InP/InGaAs heterojunction bipolar transistors (HBT's) with a base doping concentration of 1×10² 0 cm^-3. We obtained f_T of 161 GHz and f_max of 167 GHz with a 2×10 μm emitter. These high values indicate the best performance of InP/InGaAs HBT's ever reported, in so far as we know. These values were attained by reducing the base resistance using ALE/MOCVD and base-collector capacitance using a new SA process. These results indicate the great potential of these devices for ultrahigh-speed application     

Comparison of DC and high-frequency performance of zinc-doped andcarbon-doped InP/InGaAs HBTs grown by metalorganic chemical vapordeposition

Zinc and carbon-doped InP/InGaAs heterojunction bipolar transistors (HBTs) with the same design were grown by metalorganic chemical vapor deposition (MOCVD). DC current gain values of 36 and 16 were measured for zinc and carbon-doped HBTs, respectively, and carrier lifetimes were measured by time-resolved photoluminescence to explain the difference. Transmission line model (TLM) analysis of carbon-doped base layers showed excellent sheet-resistance (828 Ω/□ for 600 A base), indicating successful growth of highly carbon-doped base (2×10¹⁹ cm^-3). The reasons for larger contact resistance of carbon than zinc-doped base despite its low sheet resistance were analyzed. f_T and f_max of 72 and 109 GHz were measured for zinc-doped HBTs, while 70-GHz f_T and 102 GHz f_max were measured for carbon-doped devices. While the best performance was similar for the two HBTs, the associated biasing current densities were much different between zinc (4.0×10 ⁴ A/cm²) and carbon-doped HBTs (2.0×10⁵ A/cm²). The bias-dependant high-frequency performance of the HBTs was measured and analyzed to explain the discrepancy     

Carbon-doped base GaAs-AlGaAs HBT's grown by MOMBE and MOCVDregrowth

High-quality GaAs-AlGaAs heterojunction bipolar transistors (HBTs) in which the carbon-doped base layers (p=10¹⁰-10²⁰ cm^-3, 400-800 Å thick) and Sn-doped collector and subcollector layers are grown by metalorganic molecular-beam epitaxy (MOMBE) and a subsequent regrowth using metalorganic chemical vapor deposition (MOCVD) is used to provide the n⁺ AlGaAs emitter and GaAs/InGaAs contact layers are discussed. A current gain of 20 was obtained for a base doping of 10¹⁹ cm^-3 (800 Å thick) in a 90-μm-diameter device, with ideality factors of 1.0 and 1.4 for the base-collector and emitter-base junctions, respectively, demonstrating the excellent regrowth-interface quality. For a base doping of 10²⁰ cm^-3 (400 Å thick), the current gain decreased to 8     

Role of dopant incorporation in low-temperature Si epitaxial growthby rapid thermal processing chemical vapor deposition

The authors have demonstrated that epitaxial growth temperatures can be lowered by dopant incorporation using rapid thermal processing chemical vapor deposition. Heavily As- and B-doped epitaxial layers with very abrupt dopant transition profiles and relatively uniform carrier distributions have been grown at 800°C. The film quality and defect formation were strongly dependent on the electrically active dopant concentration. The defect density as a function of electron concentration shows a sharp transition at 3×10¹⁸ cm^-3 for As-doped epitaxy. For B-doped epitaxy, the film quality was monocrystalline with smooth surface morphology for hole concentrations above 5×10¹⁹ cm^-3     

A study of frequency response in silicon heterojunction bipolartransistors with amorphous silicon emitters

A detailed physical model of amorphous silicon (a-Si:H) is incorporated into a two-dimensional device simulator to examine the frequency response limits of silicon heterojunction bipolar transistors (HBT's) with a-Si:H emitters. The cutoff frequency is severely limited by the transit time in the emitter space charge region, due to the low electron drift mobility in a-Si:H, to 98 MHz which compares poorly with the 37 GHz obtained for a silicon homojunction bipolar transistor with the same device structure. The effects of the amorphous heteroemitter material parameters (doping, electron drift mobility, defect density and interface state density) on frequency response are then examined to find the requirements for an amorphous heteroemitter material such that the HBT has better frequency response than the equivalent homojunction bipolar transistor, We find that an electron drift mobility of at least 100 cm² V^-1 s^-1 is required in the amorphous heteroemitter and at a heteroemitter drift mobility of 350 cm ² V^-1 s^-1 and heteroemitter doping of 5×10¹⁷ cm^-3, a maximum cutoff frequency of 52 GHz can be expected     

Minority-carrier transport parameters in heavily doped p-typesilicon at 296 and 77 K

Minority-carrier electron lifetime, mobility and diffusion length in heavily doped p-type Si were measured at 296 and 77 K. It was found that a 296 K μ_n (pSi)≈μ_n (nSi) for N _AA≲5×10¹⁸ cm^-3, while μ_n (pSi)/μ_n (nSi)≈1 to 2.7 for higher dopings. The results also show that for N_AA≲3×10¹⁹ cm^-3, D (pSi) at 77 K is smaller than that at 296 K, while for higher dopings D_n (pSi) is larger at 77 K than at 296 K. μ_n (pSi) at 77 K increases with the increasing doping above N_AA>3×10¹⁸ cm^-3, in contrast to the opposite dependence for μ_n (nSi) in n⁺ Si