Simulation study of the DC and AC characteristics of an a-Si:H(n)/GaAs(p)/GaAs(n) heterojunction bipolar transistor

This paper presents the results of a simulation study focused on the evaluation of the fundamental DC and high-frequency characteristics of a GaAs-based heterojunction bipolar transistor employing a wide gap emitter made of hydrogenated amorphous silicon (a-Si:H). The role of the fundamental geometric design parameters on the device performance is analysed, showing in particular that the emitter thickness has a strong impact on the DC current gain, while the base thickness weakly affects the cut-off frequency. The role of the electronic properties of the thin film amorphous emitter is also discussed, leading to the conclusion that the device AC characteristics are in fact principally limited by the poor carrier mobility typical of a-Si:H. However, a DC current gain of 4000 and a cut-off frequency close to 10 GHz can be predicted for an optimised device if standard values for the electronic parameters of the materials are assumed.     

Substrate orientation and processing effects on GaAs/Si misorientation in GaAs-on-Si grown by MBE

The angular misorientation of GaAs epitaxial layers grown on silicon substrates by molecular beam epitaxy has been measured using x-ray diffraction. A significant misorientation, or tilt, between the epitaxial layer and the substrate has been observed. The magnitude of the tilt depends on the initial substrate orientation, the silicon substrate type (float zone or Czochralski), postgrowth annealing, and epitaxial layer thickness. In almost all cases, the sense of the tilt is such that the GaAs 〈001〉 lies between the surface normal and the silicon 〈001〉. While the presence of interfacial dislocations with Burgers vectors that are approximately parallel to the heterointerface does predict a tilt between the substrate and the epitaxial layer, the sense of the tilt that arises from these dislocations is opposite to that observed experimentally. A model, based on the relief of misfit by dislocations inclined approximately 45 degrees to the interface, is proposed that correctly describes the observed tilt.     

Passivation of carbon acceptors during growth of carbon-doped GaAs,InGaAs, and HBTs by MOCVD

Carbon dopedp-type GaAs and In_0.53Ga_0.47As epitaxial layers have been grown by low-pressure metalorganic chemical vapor deposition using CC1₄ as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In_0.53Ga_0.47As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 × 10²⁰ cm⁻³ after a 5 minute anneal at ≈400° C in N₂, while the hole concentration in In_0.53Ga_0.47As reached 1.6 × 10¹⁹ cm⁻³ after annealing. This annealing behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH₃/H₂ ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at ≈625° C. The effect ofn-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at ≈525° C shows that hydrogen can come from AsH₃, PH₃, or H₂, and can be incorporated during growth and during the post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region.     

Localized deposition of GaAs/GaInP heterostructures using LP-MOVPE

GaInP layers were grown selectively by low pressure MOVPE in patterned SiO₂ masks on GaAs (100) substrates. The variation of the composition and spontaneous ordering phenomena were analysed by Raman spectroscopy and photoluminescence. In contrast to GaInAs, the composition of GalnP shows only a very weak dependence on the size of the structures. On the other hand, there is a shift of the bandgap energy up to 40 meV with decreasing size of the stripes caused by ordering of the Ga and In atoms. Based on these findings lattice matched GaAs/GalnP multilayers were grown to delineate the growth history of the structures. It was demonstrated that the growth habit of deposition in narrow slits (>1μm) can be used to produce mesa-like stripes with dimensions below 100 nm on top of the mesa. Results of GaAs/GaInP quantum wells selectively grown on top of a mesa are presented.     

Effects of high temperature annealing on the device characteristics of Ga0.52In0.48P/GaAs and Al0.52In0.48P/GaAs heterojunction bipolar transistors

GaInP/GaAs and AlInP/GaAs heterojunction bipolar transistor (HBT) structures were grown by low pressure metalorganic vapor phase epitaxy and annealed at various temperatures up to 675°C for 15 min. Subsequent comparisons with HBTs fabricated on both annealed and unannealed control samples showed no effects for annealing up to and including 575°C, but significant changes in the electrical characteristics were observed at an annealing temperature of 675°C. For the GaInP/GaAs devices, the base current increased by a significant amount, reducing the gain and increasing the base current ideality factor from 1.07 to 1.9. Photoluminescence and electrical measurements on the structures indicated that both the emitter and base were affected by an increase in the recombination times in those regions. These effects were attributed to an out-diffusion of hydrogen from the base during annealing. The emitter of the AlInP/GaAs HBT was affected less by the hydrogen diffusion because of the larger bandgap. These observations have important implications for device performance dependence on the details of the temperature/time profile subsequent to the base growth.     

First hydride free GaInP/GaAs carbon doped HBT grown by CBE usingDMAAs and TBP

A current gain of 120, for a base sheet resistance of 400 Ω/□, is reported in a carbon doped base heterojunction bipolar transistor grown by chemical beam epitaxy (CBE) without hydride sources. This result is to the authors' knowledge, the best obtained with hydride free CBE for this device     

高速AlGaAs/GaAs HBT D-触发器和静态分频器

叙述了高速 Al Ga As/ Ga As HBT D-触发器和静态分频器的设计、制造和性能。用电流型逻辑和自对准工艺 ,D-触发器上升和下降时间都小于 80 ps,静态分频器在 0～ 8GHz频率范围功能正确     

InGaP/GaAs HBT器件的制备及其特性

采用在发射区台面腐蚀时保留InGaP钝化层和去除InGaP钝化层的方法制备了两种InGaP/GaAs异质结双极晶体管(HBT)器件,研究了InGaP钝化层对HBT器件基区表面电流复合以及器件直流和射频微波特性的影响.对制备的两种器件进行了对比测试后得到:保留InGaP钝化层的HBT器件最大直流增益(β)为130,最高振荡频率(fmax)大于53 GHz,功率附加效率达到61％,线性功率增益为23 dB;而去除InGaP钝化层的器件最大β为50,fnax大于43 GHz,功率附加效率为57％,线性功率增益为18 dB.测试结果表明,InGaP钝化层作为一种耗尽型的钝化层能有效抑制基区表面电流的复合,提高器件直流增益,改善器件的射频微波特性.     

新结构InGaP/GaAs/InGaP DHBT生长及特性研究

设计并生长了一种新的InGaP/GaAs/InGaP DHBT结构材料,采用在基区和集电区之间插入n+-InGaP插入层结构,以解决InGaP/GaAs/InGaP DHBT集电结导带尖峰的电子阻挡效应问题。采用气态源分子束外延(GSMBE)技术,通过优化生长条件,获得了高质量外延材料,成功地生长出带有n+-InGaP插入层结构的GaAs基InGaP/GaAs/InGaP DHBT结构材料。采用常规的湿法腐蚀工艺,研制出发射极面积为100μm×100μm的新型结构InGaP/GaAs/InGaP DHBT器件。直流特性测试的结果表明,所设计的集电结带有n+-InGaP插入层的InGaP/GaAs/InGaP DHBT器件开启电压约为0.15V,反向击穿电压达到16V,与传统的单异质结InGaP/GaAs HBT相比,反向击穿电压提高了一倍,能够满足低损耗、较高功率器件与电路制作的要求。     

OMVPE grown GalnAs: C for HBTs

We have grown GaInAs:C by low pressure organometallic vapor phase epitaxy and observed that the hole concentration of such layers decreases upon growth of cap layers such as heterojunction bipolar transistor emitter layers. Two mechanisms were found to play a role: one is H repassivation of the C_As acceptors, the other a non-H related decrease in the concentration of C_As acceptors due to C changing site or to the formation of complexes involving C_As. Depending on the growth conditions of the cap layers (temperature, flow of group V sources), one or the other mechanism prevails.     

钝化边沿的制作及其对GaInP／GaAs SHBT性能的影响

利用光刻胶形成保护侧墙，用湿法腐蚀来形成发射极钝化边沿。这种方法工艺简单，不需要额外的绝缘介质作为掩膜，也不需要双层腐蚀终止层。研发出了带发射极钝化边沿的GaInP／GaAs单异质结双极型晶体管（SHBT），并对不同尺寸有无钝化边沿的器件特性进行对比，结果表明钝化边沿能有效改善小尺寸器件的直流特性，对器件的高频特性无明显影响。     

Ge组分对SiGe HBT直流特性的影响

制作了基区Ge组分分别为0.20和0.23的多发射极指数双台面结构SiGe异质结双极型晶体管(HBT)。实验结果表明,基区Ge组分的微小增加,引起了较大的基极复合电流,但减小了总的基极电流,提高了发射结的注入效率,电流增益成倍地提高。Ge组分从0.20增加到0.23,HBT的最大直流电流增益从60增加到158,提高了约2.6倍。     

Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction

We have optimized the base electrode for InGaAs/InP based double heterojunction bipolar transistors with a buried emitter-base junction. For the buried emitter-base structure, the base metal is diffused through a thin graded quaternary region, which is doped lightly n-type, to make ohmic contact to the p⁺InGaAs base region. The metal diffusion depth must be controlled, or contact will also be made to the collector region. Several metal schemes were evaluated. An alloy of Pd/Pt/Au was the best choice for the base metal, since it had the lowest contact resistance and a sufficient diffusion depth after annealing. The Pd diffusion depth was easily controlled by limiting the thickness to 50?, and using ample Pt, at least 350?, as a barrier metal to the top layer of Au. Devices with a 500? base region show no degradation in dc characteristics after operation at an emitter current density of 90 kA/cm² and a collector bias, V_CE, of 2V at room temperature for over 500 h. Typical common emitter current gain was 120. An f_t of 95 GHz and f_max, of 131 GHz were achieved for 2×4 μm² emitter size devices.     

Prevention of thermal surface damage in GaAs by encapsulated annealing in an arsine ambient

This paper shows that both capped and capless techniques commonly used in the high temperature annealing of GaAs can cause thermal surface damage characterized by a decrease in the net carrier concentration in a region within a few micrometers of the surface. This thermal surface damage can be prevented by a technique of encapsulated annealing in an arsine ambient. Presented at the 26th Annual Electronic Materials Conference, Santa Barbara, CA, June 21, 1984.     

Reconstruction of excitonic spectrum during annealing of ZnSe:N grown by metalorganic vapor phase epitaxy

The reconstruction of the bound excitonic spectra of MOVPE-grown ZnSe:N samples caused by thermal annealing was observed. The results of the low temperature photoluminescence, reflection and SIMS measurements show that this reconstruction is caused neither by the strain effect nor by the removal of hydrogen from the samples. The calculation of the defect structure and energy by the SCF MO LCAO method was carried out, and a new stable configuration of the N_se center has been found. A model of reconstruction of the nitrogen centers is proposed, assuming that the transition of N_Se centers from a less stable state with distorted T_d configuration into the energetically more favorable distorted C_3v configuration occurs due to thermal annealing, resulting in the corresponding changes in the luminescence spectra.     

Thermal annealing effects on p-type conductivity of nitrogendoped ZnSe grown by metalorganic vapor phase epitaxy

Post-growth thermal annealing (e.g., 500°C, 30 min), is proposed as one of the promising techniques to realize and to improve the quality of p-type ZnSe layers grown by metalorganic vapor phase epitaxy (MOVPE). The layers were grown at low temperature (350°C) by photo-assisted MOVPE with doping nitrogen from tertiarybutylamine (t-BuNH₂). The flow rate of t-BuNH₂ was limited to be relatively low, in order to avoid heavy doping, with which as-grown layers exhibited electrically high-resistivity; but the thermal annealing converted the layers to p-type. As the as-grown layers exhibited the stronger donor-to-acceptor pair recombination lines or the weaker donor-bound excitonic emission (I_x) lines in photoluminescence, the annealed layers resulted in higher net acceptor concentration, which was 1 x 10¹⁷ cm⁻⁴ at the optimum conditions at present.     

HBT自热效应对功率放大器偏置电路的影响及补偿

研究了GaAs HBT的自热效应对功率放大器镜像电流源偏置电路性能的影响.HBT自热效应使得这种偏置电路的镜像精度和温度特性变差.利用HBT器件特有的集电极电流热电负反馈理论,通过优化基极偏置电阻的方法,对自热效应进行了有效补偿,偏置电路的电流镜像精度得到有效提高,偏置电流温度漂移由9.5%减小到0.5%.     

Thermal characteristics of InP, InAlAs, and AlGaAsSb metamorphic buffer layers used in In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors grown on GaAs substrates

In_0.52Al_0.48As/In_0.53Ga_0.47As heterojunction bipolar transistors (HBTs) were grown metamorphically on GaAs substrates by molecular beam epitaxy. In these growths, InAlAs, AlGaAsSb, and InP metamorphic buffer layers were investigated. The InAlAs and AlGaAsSb buffer layers had linear compositional grading while the InP buffer layer used direct binary deposition. The transistors grown on these three layers showed similar characteristics. Bulk thermal conductivities of 10.5, 8.4, and 16.1 W/m K were measured for the InAlAs, AlGaAsSb, and InP buffer layers, as compared to the 69 W/m K bulk thermal conductivity of bulk InP. Calculations of the resulting HBT junction temperature strongly suggest that InP metamorphic buffer layers should be employed for metamorphic HBTs operating at high power densities.     

Extraction of small-signal equivalent circuit model parameters for Si/SiGe HBT using S-parameters measurements and one geometrical information

A physical and simple method is proposed to extract the hybrid-π small-signal equivalent circuit model of Si/SiGe heterojunction bipolar transistor (HBT). In this method, we use test (dummy) structures to extract by means of fitting techniques the extrinsic bias-independent parameters representing the contact pads plus the transmission line connections to the core of the active device. All intrinsic bias-dependent parameters are calculated analytically from S-parameters only. The ratio of the area of the emitter contact to base area is used to solve the base–collector feedback problem due to the distributed nature of the base. Using this physical (geometry) constraint instead of the measured direct current (DC) information helps to get more reliable parameters and easier calculations. When we applied this methodology, a good agreement is obtained between the modelled S-parameters with the corresponding measured ones over the broad band from 40 MHz to 20.02 GHz. The error for three different bias points was less than 1.2%.     

Intersubband absorption characteristics in OMVPE grown delta-doped GaAs/AlGAs multiple quantum well structures

A study was carried out using a series of multiple quantum well structures grown by organometallic vapor phase epitaxy (OMVPE) to evaluate the intersubband absorption characteristics, thus enabling a direct correlation of the delta doping parameters to device performance. Significant improvements in the absorption characteristics were obtained by adopting a localized delta-doping profile in the absorption quantum wells as opposed to homogeneously doped structures. The transition linewidths were observed to decrease from 40 meV in the uniformly doped sample to 20 meV in devices in corporating delta-doped quantum wells. In addition, the measured absorption strengths of the intersubband resonance grew in a linear fashion as the carrier sheet density in the well was increased to approximately 2 × 10¹² cm⁻².