Velocity-modulation and transit-time effects in InP/InGaAs HBTs

The base-collector capacitance C_bc and the collector transit time delay τc govern the high-speed performance of modern heterojunction bipolar transistors (HBTs). Both are shown to be strongly modified by velocity modulation effects in InP/InGaAs HBTs: The carrier velocity in the collector depends on V_cb and I_c, causing a reduction of C_bc and τc respectively. The current induced transit time modulation is shown to be conveniently expressed by a minor but important modification of the conventional transit time delay expression. Particle simulations are performed to assess the relevance of these effects     

Enhancement of fmax in InP/InGaAs HBTs by selectiveMOCVD growth of heavily-doped extrinsic base regions

InP/InGaAs heterojunction bipolar transistors (HBT's) with selectively grown heavily-doped extrinsic base layers have been fabricated. A new selective metalorganic chemical vapor deposition (MOCVD) method using a very high-speed rotating susceptor, which can attain high selectivity even at low growth temperature, is employed for the extrinsic-base regrowth. The maximum f_max of the HBT with the selectively grown extrinsic-base layer is 141 GHz, which is more than 50% larger than that of a HBT without the selective growth. The base resistances are estimated by a small-signal equivalent-circuit analysis and transmission line model measurements, and we find that the resistance is reduced to be about a half by the selective regrowth. This significant reduction is achieved by the decrease of base contact resistance as well as the low regrowth-interface resistance. We also discuss Zn redistribution during the extrinsic base regrowth     

Investigation of the degradation of InGaAs/InP double HBTs underreverse base-collector bias stress

In this paper, we report on the degradation of DC performance of InP/InGaAs/InP double heterojunction bipolar transistors (DHBTs) during electrical stress. Devices with different sizes were investigated under highly reverse base-collector (B-C) bias stress. The increase of B-C and emitter-base (E-B) junction leakage and decrease of current gain were observed. The increase of the junction leakage for both B-C and E-B junctions was found to scale with the junction perimeters which suggests that the stress-induced damages are localized at the junction peripheries. For the devices with larger emitter periphery-to-area ratio, a more pronounced decrease of current gain due to the stress was observed. The obtained experimental data indicate that the stress-induced degradation happens in high reverse B-C bias voltage (avalanche) regime. The degradation is believed to be induced by hot carriers rather than current. A physical model is proposed to explain the experimental observations     

Specific contact resistivity of InGaAs/InP p-isotype heterojunctions

The specific contact resistivity of lattice matched InGaAs/InP p-isotype heterojunction has been measured through the use of an interface transmission line model structure. The measured resistance values are comparable to or greater than those of the metal/semiconductor interface and depend heavily on the doping and the abrupt or graded nature of the interface.<>     

A comparison between Monte Carlo and extended drift-diffusionmodels for abrupt InP/InGaAs HBTs

In this paper, a comparison between the simulation results of abrupt InP/InGaAs n-p-n heterojunction bipolar transistors (HBTs) obtained from both an extended drift-diffusion (EDD) model and from a Monte Carlo (MC) HBT simulator is carried out. The EDD approach is based on Grinberg's model for the electron current through the interfacial emitter-base spike-like potential barrier. The MC procedure includes the effects of quantum transmission/reflection through the abrupt heterojunction. The transmission coefficient is obtained from a numerical solution of Schrodinger's equation (self-consistently embedded in the general MC procedure) that takes into account the nonparabolicity of the bands and the spatial change in the effective mass. The differences between both models and their physical causes are also analyzed in this paper. It Is shown that, for the HBT under consideration, the collector current is determined by the transmission of electrons through the spike, while the numerical values of the parameters associated with the transport mechanisms in the base region have a very small influence on the collector current. An alternative equation to the conventional diffusion current equation in the neutral base region has also been developed, which includes the hot electron effects     

Improved InP/InGaAs/InP PIN detector response using a transparent conductor contact

The elimination of the spatial variation in the frequency response of large area pin photodetectors is described using indium tin oxide as a transparent contact. The I/V, C/V, and relative frequency response characteristics are reported for devices fabricated with and without the indium tin oxide. The devices have active area diameters of 25.0 and 80.0 mu m. Responsivities were 0.53 and 0.61 A/W for photodetectors with and without the ITO contact, respectively.<>     

Measurement of base and collector transit times in thin-base InGaAs/InP HBT

The influence of base thickness reduction on performances of heterojunction bipolar transistors (HBTs) is examined. HBT structures are grown, with a base thickness in the range 25-65 nm and doping concentration from 3/spl times/10/sup 19/ to 6/spl times/10/sup 19/ at/cm/sup 3/. Base transit time is accurately extracted from total base-collector transit time, and described using a simple drift-diffusion approach. This model, however basic, shows very good agreement with measurements when usual parameter values are used. A 0.13-ps transit time reduction is measured when thinning the base from 65 to 25 nm. The thinnest base structure presents a 0.08 ps transit time, allowing a 250 GHz f/sub t/ operation at 270 kA/cm/sup 2/ emitter current density.     

InP/InGaAs heterojunction phototransistors

We describe the fabrication and device characteristics of experimental back-illuminated InP/InGaAs n-p-n heterojunction phototransistors. These devices exhibit photoresponse in the wavelength range of0.95-1.6 mum. An optical gain of 40 at an input power of 1 nW (an improvement of 1000 in sensitivity over previously reported phototransistors) has been observed. Gains as high as 1000 have been achieved for higher incident power levels.     

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     

高速InP/InGaAs HBT

<正> 最近TI公司报道了一种甚高性能的InP/InGaAs HBT,其f_(max)为180GHz,f_T为100GHz,电流密度为1×10~5A/cm~2。有效延迟时间(f_T/8πf_(max)~2)为0.2ps,这是已报道的共发射极InP/InGaAsHBT中的最小值。 这     

Measurements of the InGaAs hole impact ionization coefficient inInAlAs/InGaAs pnp HBTs

The hole multiplication factor in pnp InAlAs/InGaAs single heterojunction bipolar transistors (HBTs) has been measured as a function of the base-collector bias. The hole impact ionization coefficient β_p has been estimated taking into account the Early effect, I_CBO, and thermal effects. Numerical corrections for dead space were made. The importance of considering second order effects is highlighted, showing that rough approximations can lead to an overestimation of the coefficient β_p. At low electric fields, the extracted coefficient agrees with the most recent photomultiplication measurements available in the literature. At high electric fields, hole impact ionization coefficient is estimated up to values previously not reported in the literature (β_p≈10⁴ cm^-1)     

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     

Facet oxidation of InGaAsP/InP and InGaAs/InP lasers

The facet oxidation of InGaAsP/InP and InGaAs/InP lasers is investigated after aging under high constant optical output power or high current stress. Facet oxidation in InGaAsP/InP lasers is negligibly small under several thousand hours of practical operation. The thickness of oxide film increases in proportion to optical output power and logarithm of aging time. The growth rate of facet oxide film weakly depends on the junction temperature and the activation energy is estimated to be 0.07 eV within a experimental range between 25 and 150°C. The facet of InGaAs/InP lasers are oxidized more easily than that of InGaAsP/InP lasers but are about two orders of magnitude more stable against oxidation than that of AlGaAs/GaAs lasers.     

Quantifying neutral base recombination and the effects ofcollector-base junction traps in UHV/CVD SiGe HBTs

This work quantifies neutral base recombination in UHV/CVD SiGe heterojunction bipolar transistors (HBTs) using calibrated two-dimensional (2-D) simulation. The simulated collector-base conductance through neutral base recombination (NBR) modulation is far below the experimentally observed values, and hence does not explain the measured output resistance degradation under forced-I_B operation. In spite of the output resistance degradation, these UHV/CVD SiGe HBTs have approximately the same base current as the silicon control, and hence higher current gain. Based on the observation of the majority carrier concentration limited recombination in the CB junction depletion layer, as opposed to the minority carrier concentration limited recombination in the neutral base, local presence of traps in the CB junction depletion layer is suggested. This explains the measured CB conductance modulation and the related output resistance degradation without compromising the current gain. Numerical simulations using traps locally introduced into the CB junctions successfully reproduced the measured collector-base conductance from simulation without appreciable degradation in current gain     

异质结InP/InGaAs探测器欧姆接触温度特性研究

为了研究异质结InP/InGaAs探测器帽层的欧姆接触特性,采用Au/p-InP传输线模型(TLM),对比不同退火温度下的接触特性,在480℃、30 s的退火条件下实现室温比接触电阻为3.84×10~(-4)Ω·cm~2,同时,对欧姆接触的温度特性进行了研究,发现随着温度降低比接触电阻增加,在240~353 K温度范围内界面电流传输主要为热电子-场发射机制(TFE);240 K以下,接触呈现肖特基特性.利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)分别对界面处的扩散程度和化学反应进行了分析,发现经过480℃、30 s退火后样品界面处存在剧烈的互扩散,反应产物Au_(10)In_3有利于改善Au/p-InP的接触性能.     

Thermally stable Ge/Ag/Ni Ohmic contact for InAlAs/InGaAs/InP HEMTs

Excellent annealed ohmic contacts based on Ge/Ag/Ni metallization have been realized in a temperature range between 385 and 500/spl deg/C, with a minimum contact resistance of 0.06 /spl Omega//spl middot/mm and a specific contact resistivity of 2.62 /spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ obtained at an annealing temperature of 425/spl deg/C for 60 s in a rapid thermal annealing (RTA) system. Thermal storage tests at temperatures of 215 and 250/spl deg/C in a nitrogen ambient showed that the Ge/Ag/Ni based ohmic contacts with an overlay of Ti/Pt/Au had far superior thermal stabilities than the conventional annealed AuGe/Ni ohmic contacts for InAlAs/InGaAs high electron mobility transistors (HEMTs). During the storage test at 215/spl deg/C, the ohmic contacts showed no degradation after 200 h. At 250/spl deg/C, the contact resistance value of the Ge/Ag/Ni ohmic contact increased only to a value of 0.1 /spl Omega//spl middot/mm over a 250-h period. Depletion-mode HEMTs (D-HEMTs) with a gate length of 0.2 /spl mu/m fabricated using Ge/Ag/Ni ohmic contacts with an overlay of Ti/Pt/Au demonstrated excellent dc and RF characteristics.     

Fabrication of high-speed InP/InGaAs/InP DHBT with a new self-aligned metallization technique for reduced base resistance

A new self-aligned emitter–base metallization (SAEBM) technique with wet etch is developed for high-speed heterojunction bipolar transistors (HBTs) by reducing extrinsic base resistance. After mesa etch of the base layer using a photo-resist mask, the base and emitter metals are evaporated simultaneously to reduce the emitter–base gap (S_EB) and base gap resistance (R_GAP). The InP/InGaAs/InP double heterojunction bipolar transistor (DHBT) fabricated using the technique has a reduced R_GAP, from 16.48 Ω to 4.62 Ω comparing with the DHBT fabricated by conventional self-aligned base metallization (SABM) process. Furthermore, we adopt a novel collector undercut technique using selective etching nature of InP and InGaAs to reduce collector–base capacitance (C_CB). Due to the reduced R_GAP, the maximum oscillation frequency (f_max) for a 0.5 μm-emitter HBT is improved from 205 GHz to 295 GHz, while the cutoff frequency (f_T) is maintained at around 300 GHz.     

Metamorphic Heterostructure InP/GaAsSb/InP HBTs on GaAs Substrates by MOCVD

Good-quality metamorphic InP buffer layers have been successfully grown on GaAs substrates by metal-organic chemical vapor deposition. Characterization by atomic force microscope, transmission electron microscopy, high-resolution X-ray diffraction, and Hall measurements indicated that the layers are of high crystalline quality, good mobility, and excellent surface morphology. On this buffer, we demonstrated the first metamorphic InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with good material quality and device performance. Metamorphic DHBTs showed direct-current and radio-frequency characteristics that are comparable to those grown on lattice-matched InP substrates.     

InP/InAlAs/InGaAs quantum wires

Single InGaAs quantum wires and stacked InGaAs quantum wires with InAIAs barriers have been fabricated on V-grooved InP substrates by low pressure metal-organic chemical vapour deposition (MOCVD). We have found growth conditions where the InAIAs barrier exhibits a resharpening effect, similar to that of AlGaAs utilized for growth on GaAs substrates. The existence of structural and electronic quantum wires in the bottom of the grooves is proven.