AlGaAs/GaAs HBTs for 10-Gb/s ICs using a new base ohmic contactfabrication process

A new basic ohmic contact technology for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is presented. The effect of the device parameters on the high-frequency performance of HBT ICs for 10-Gb/s systems is analyzed, and it is shown that, at a cutoff frequency (f_T) of 40 GHz or more, reducing base resistance or collector capacitance is more effective than increasing f_T for obtaining high-frequency performance. A process is developed for fabricating base electrodes with a very low ohmic contact resistivity, ~10^-7 Ω-cm², by using a AuZn/Mo/Au alloy, which provides the required high performance. Self-aligned AlGaAs/GaAs HBTs, with a 2.5-μm×5-μm emitter, using a AuZn/Mo/Au alloy base metal and an undoped GaAs collector, are shown to have an f_T and a maximum oscillation frequency of about 45 and 70 GHz, respectively, at 3.5 mA. An AGC amplifier with a 20-dB gain and a bandwidth of 13.7 GHz demonstrates stable performance     

High/fmax collector-up AlGaAs/GaAsheterojunction bipolar transistors with a heavily carbon-doped basefabricated using oxygen-ion implantation

AlGaAs/GaAs collector-up heterojunction bipolar transistors (HBTs) with a heavily carbon-doped base layer were fabricated using oxygen-ion implantation and zinc diffusion. The high resistivity of the oxygen-ion-implanted AlGaAs layer in the external emitter region effectively suppressed electron injection from the emitter, allowing collector current densities to reach values above 10⁵ A/cm ². For a transistor with a 2-μm×10-μm collector, f_T was 70 GHz and f_max was as high as 128 GHz. It was demonstrated by on-wafer measurements that the first power performance of collector-up HBTs resulted in a maximum power-added efficiency of as high as 63.4% at 3 GHz     

Low-resistance self-aligned Ti-silicide technology for sub-quartermicron CMOS devices

A low-resistance self-aligned Ti-silicide process featuring selective silicon deposition and subsequent pre-amorphization (SEDAM) is proposed and characterized for sub-quarter micron CMOS devices. 0.15-μm CMOS devices with low-resistance and uniform TiSi₂ on gate and source/drain regions were fabricated using the SEDAM process. Non-doped silicon films were selectively deposited on gate and source/drain regions to reduce suppression of silicidation due to heavily-doped As in the silicon. Silicidation was also enhanced by pre-amorphization, using ion-implantation, on the narrow gate and source/drain regions. Low-resistance and uniform TiSi₂ films were achieved on all narrow, long n⁺ and p⁺ poly-Si and diffusion layers of 0.15-μm CMOS devices. TiSi₂ films with a sheet resistance of 5 to 7 Ω/sq were stably and uniformly formed on 0.15-μm-wide n⁺ and p⁺ poly-Si. No degradation in leakage characteristics was observed in pn-junctions with TiSi₂ films. It was confirmed that, using SEDAM, excellent device characteristics were achieved for 0.15-μm NMOSFET's and PMOSFET's with self-aligned TiSi₂ films     

InGaAs/InAlAs/InP collector-up microwave heterojunction bipolartransistors

Collector-up InGaAs/InAlAs/InP heterojunction bipolar transistors (HBTs) were successfully fabricated, and their DC and microwave characteristics measured. High collector current density operation (J_c>30 kA/cm²) and high base-emitter junction saturation current density (J₀>10^-7 A/cm²) were achieved. A cutoff frequency of f _t=24 GHz and a maximum frequency of oscillation f _max=20 GHz at a collector current density of J₀ =23 kA/cm² were achieved on a nominal 5-μm×10-μm device     

Experimental values for the hole diffusion coefficient andcollector transit velocity in P-n-p AlGaAs/GaAs HBTs

The diffusion coefficient (D_h) and a value for the collector velocity (v_h) of holes in AlGaAs/GaAs P-n-p HBTs (heterojunction bipolar transistors) were obtained from high-frequency measurements on structures with different base and collector widths. Quantities for D_h and v _h of 5.6 cm²/s and 5.5×10⁶ cm/s, respectively, were obtained by plotting the total emitter-collector delay versus inverse emitter current and extrapolating the data to infinite emitter current to obtain the base and collector transit delays. An f_t and f_max as high as 15 and 29 GHz, respectively, were obtained for non-self-aligned (1-μm emitter mesa/base contact separation) devices with a 2.6-μm×10-μm emitter     

InP/InGaAs HBTs with n+-InP contacting layers grown byMOMBE using SiBr4

InP/InGaAs heterojunction bipolar transistors (HBTs) with low resistance, nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers have been demonstrated with excellent DC characteristics. A specific contact resistance of 5.42×10^-8 Ω·cm², which, to the best of our knowledge, is the lowest reported for TiPtAu on n-InP, has been measured on InP doped n=6.0×10¹⁹ cm^-3 using SiBr₄. This low contact resistance makes TiPtAu contacts on n-InP viable for InP/InGaAs HBTs     

1.3-μm emission of Nd:LaF3 thin films grown bymolecular beam epitaxy

The 1.3-μm emission of Nd³⁺-doped LaF₃ thin films grown on LaF₃ and CaF₂ (111) substrates by molecular beam epitaxy is reported. The waveguide behavior of the heteroepitaxial layers has been demonstrated and the refractive indexes measured. Guided spectra have been obtained from these layers using a prism-coupling technique. The 1.3-μm emission corresponding to the 4F _3/2→⁴I_3/2 transition has been characterized as a function of Nd³⁺ concentration and temperature. The relative efficiencies of different excitation bands were compared. The optimum concentration for Nd³⁺ dopant has been found to be about 1 at.%. A narrowing of the emission lines is observed in the homoepitaxial layers compared to the heteroepitaxial layers. The decay of the luminescence of the ⁴F_3/2 level measured at room temperature is similar for homoepitaxial and heteroepitaxial layers     

High-speed small-scale InGaP/GaAs HBT technology and itsapplication to integrated circuits

We have developed the advanced performance, small-scale InGaP/GaAs heterojunction bipolar transistors (HBTs) by using WSi/Ti base electrode and buried SiO₂ in the extrinsic collector. The base-collector capacitance C_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 SiO₂ region by 50% compared to our previous devices. The cutoff frequency f_T of 156 GHz and the maximum oscillation frequency f_max of 255 GHz were obtained at a collector current I_C of 3.5 mA for the HBT with an emitter size S_E of 0.5×4.5 μm², and f_T of 114 GHz and f_max of 230 GHz were obtained at I_C of 0.9 mA for the HBT with S_E of 0.25×1.5 μm². 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·Ω 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     

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     

Power performance of InP-based single and double heterojunctionbipolar transistors

The microwave and power performance of fabricated InP-based single and double heterojunction bipolar transistors (HBTs) is presented. The single heterojunction bipolar transistors (SHBTs), which had a 5000 Å InGaAs collector, had BV_CEO of 7.2 V and J_Cmax of 2×10⁵ A/cm². The resulting HBTs with 2×10 μm² emitters produced up to 1.1 mW/μm2 at 8 GHz with efficiencies over 30%. Double heterojunction bipolar transistors (DHBTs) with a 3000-Å InP collector had a BV_CEO of 9 V and J_{c max} of 1.1×10⁵ A/cm², resulting in power densities up to 1.9 mW/μm² at 8 GHz and a peak efficiency of 46%. Similar DHBTs with a 6000 Å InP collector had a higher BV_CEO of 18 V, but the J _{c max} decreased to 0.4×10⁵ A/cm² due to current blocking at the base-collector junction. Although the 6000 Å InP collector provided higher f_max and gain than the 3000 Å collector, the lower J_{c max} reduced its maximum power density below that of the SHBT wafer. The impact on power performance of various device characteristics, such as knee voltage, breakdown voltage, and maximum current density, are analyzed and discussed     

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     

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     

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     

Increasing the current density of dielectric-base transistors withan MgO emitter-base barrier

We measured the current-voltage characteristics of YBa₂Cu₃O_7-x/oxide/n-SrTiO₃ diodes using NdGaO₃, LaAlO₃, CeO₂, and MgO as the oxide. MgO films had the highest current density. We then fabricated dielectric-base transistors with a YBa₂Cu₃ O_7-x(YBCO) emitter/collector on a SrTiO₃ dielectric base with an MgO barrier. The transistors had both voltage and current gains exceeding unity at 4.2 K. The emitter current density was about 4×10³ A/cm² at a collector-emitter voltage of 10 V and base-emitter voltage 10 V; this is 2 to 3 orders of magnitude larger than that of transistors with NdGaO₃ emitter-base barrier. We obtained a transconductance of around 0.4 mS at a collector-emitter voltage of 10 V for a device with a 6-μm-diameter emitter     

Monolithic Integration of InP HBTs and Uni-Traveling-Carrier Photodiodes Using Nonselective Regrowth

This paper describes the monolithic integration of InP HBTs and uni-traveling-carrier photodiodes (UTC-PDs) by nonselective regrowth. HBTs are fabricated from nonselectively regrown device layers and UTC-PD subcollector layers, which are grown first on a 3-in InP substrate. This makes it possible to optimize the layer design for the HBTs and UTC-PDs independently and minimize the interconnection between them. The fabricated HBTs have a collector thickness of 200 nm, and they show an f_t of 260 GHz and an f_max of 320 GHz at a collector current density of 2.5 mA/mum². The standard deviations of the f_t and f_max across the wafer are 1.7% and 4.4%, respectively. The length of the interconnection between the HBTs and UTC-PDs can be made as small as 10 mum without any degradation of the regrown-HBT performance. The UTC-PDs fabricated on the same wafer exhibit a 3-dB bandwidth of 100 GHz and an output voltage of 1.0 V. There is no drawback in the performance of either device, as compared with that of discrete devices. We also demonstrate 100-GHz optical-input divide-by-two optoelectronic integrated circuits (OEICs) consisting of InP HBTs and a UTC-PD using this technique. These results indicate that the nonselective regrowth is promising for application toward over 100-Gb/s OEICs.     

Near-ideal I-V characteristics of GaInP/GaAsheterojunction bipolar transistors

GaInP/GaAs heterojunction bipolar transistors (HBTs) have been fabricated and these devices exhibit near-ideal I-V characteristics with very small magnitudes of the base-emitter junction space-charge recombination current. Measured current gains in both 6-μm×6-μm and 100-μm×100-μm devices remain constant for five decades of collector current and are greater than unity at ultrasmall current densities on the order of 1×10^-6 A/cm². For the 6-μm×6-μm device, the current gain reaches a high value of 190 at higher current levels. These device characteristics are also compared to published data of an abrupt AlGaAs/GaAs HBT having a base layer with similar doping level and thickness     

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     

Nitrogen-implanted SiC diodes using high-temperature implantation

6H-SiC diodes fabricated using high-temperature nitrogen implantation up to 1000°C are reported. Diodes were formed by RIE etching a 0.8-μm-deep mesa across the N⁺/P junction using NF₃/O₂ with an aluminum transfer mask. The junction was passivated with a deposited SiO₂ layer 0.6 μm thick. Contacts were made to N⁺ and P regions with thin nickel and aluminum layers, respectively, followed by a short anneal between 900 and 1000°C. These diodes have reverse-bias leakage at 25°C as low as 5×10^-11 A/cm² at 10 V     

Emitter injection and collector current ideality in abrupt heterojunction AlInAs/GaInAs HBTs

We investigated the electron injection process for high-speed N-p-n AlInAs/GaInAs HBTs by measuring collector and base currents as a function of base-emitter voltage with collector-base voltage equal to zero (Gummel plots) at temperatures from 77 to 300 K. We compared the measured collector current with calculations based on electron injection from emitter to base by tunneling through the conduction band spike and thermionic emission over it, using a modified version of the thermionic-field emission theory developed by Crowell and Rideout. Good agreement was obtained between the experimental collector current ideality factor and tunneling-thermionic emission theory for all temperatures and currents. This is an improvement over drift-diffusion and thermionic emission models, which have been used for HBTs but which do not correctly describe the experimentally observed temperature and current dependence of the ideality of the collector current. The tunneling-thermionic emission model explains the increase in collector current ideality factor that occurs as the transistor is biased at high collector current density (J_C 10⁵ A cm⁻²), which is the regime of operation in which f_T is maximized and a low ideality factor is most important. The model also explains the experimentally observed variation of h_FE with ln I_C. Thus the tunneling-thermionic emission model is a useful aid in the design of the epitaxial structure for high-frequency HBTs.     

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%