High reliability sputtered Schottky diodes on GaAs

We describe developments to improve reliability and power handling for high frequency applications in whisker-contacted Schottky barrier diode mixers, detectors and multipliers fabricated using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSi_x/GaAs contacts respectively.     

GaAs monolithic Schottky junction pairs for W-band crossbar mixers

A GaAs monolithic planar chip consisting of two antiparallel Schottky junctions has been designed, processed and tested as a millimetre-wave crossbar mixer. The planar chip exhibited a broadband RF performance with a low conversion loss of 5.2013;70dB and noise temperature of 750 K at 94 GHz. The structure also exhibits a high burnout capability at W-band frequencies.     

A reliability comparison of InGaP/GaAs HBTs with and without passivation ledge

InGaP/GaAs heterojunction bipolar transistors (HBTs) with and without passivation ledge in the extrinsic base region were investigated. Gummel plot changes before and after reliability testing were compared. The experimental results demonstrated that the devices featuring the lower quality of the extrinsic base surface are more sensitive to a temperature–current stress. The HBTs with a passivation ledge have an activation energy of 1.41 eV and a mean time to failure (MTTF) of 10⁶ h whereas the HBTs without passivation ledge have an activation energy of 1.24 eV and a MTTF of 10⁵ h.     

Surface passivation of GaAs MESFETs

The metal semiconductor field effect transistor (MESFET) represents a more realistic test for “passivation” efficacy than conventional capacitor test structures due to its prototypical fabrication process. This paper evaluates Gallium-Arsenide (GaAs) surface passivation films utilizing the MESFET as a test vehicle. For this study, gate-to-drain leakage current, gate-to-drain breakdown voltage, complex impedance versus frequency, and low-frequency noise measurements are performed on MESFETs with various passivation films. The results indicate that a hydrogen plasma used to “pre-clean” the GaAs surface in conjunction with an in situ plasma-enhanced chemical vapor deposition (PECVD) Si₃N₄ passivation film yields the best performance. In contrast, atomic-layer-epitaxial ZnSe demonstrated inferior performance (even in comparison to PECVD Si₃N₄ passivation films that did not receive a hydrogen “pre-clean”)     

Fabrication and performance of GaAs p+n junction and Schottky barrier millimeter IMPATT's

A recently developed procedure, incorporating both preferential electrochemical etching for wafer thinning and electroplating for heat sink formation has been applied to the fabrication of Kaband (26.5-40 GHz) GaAs IMPATT's. Both epitaxially grown GaAs p⁺n junction and Cr Schottky barrier diodes have been fabricated. This procedure makes possible the batch fabrication of small area diodes (<2 times 10^{-5}cm²) over a large wafer area. The diodes have been operated both in the oscillator and stable-amplifier mode. Power, efficiency, and noise performance of the devices is reported. The p⁺n diodes, which could withstand junction temperature of over 300°C, gave the best power and efficiency. Powers as high as 680 mW with 12.4 percent efficiency at 34.8 GHz and an efficiency as high as 16 percent with 390 mW at 29.5 GHz have been achieved. The Cr Schottky diodes were unable to withstand junction temperatures in excess of 200°C and therefore produced less power despite the potentially better power handling capability. The highest power obtained from a Cr Schottky is 470 mW with 12.5 percent efficiency at 34 GHz. Comparable oscillator noise performance has been obtained with both types of diode. The best AM (DSB) double sideband NSR obtained is -135 dB in a 100 Hz window at 1.5 MHz from the carrier. An rms frequency deviation as low as 13 Hz in a 100 Hz window has been observed with a power output of 164 mW at 35.4 GHz by raising the external Q to 138. A lowest FM noise measure of 23 dB was achieved by reducing output power to 16 mW. The amplifier noise figure measured for both p⁺n and Cr Schottky diodes is 26 dB.     

Sulfide passivation of GaAs power diodes

The feasibility of reducing the leakage currents of GaAs power diodes by chemically treating their surfaces in solutions of (NH₄)₂S in isopropanol is investigated. It is established that after chemical surface treatment the leakage current decreases more as the immersion time in the solution is increased (eightfold reduction) and also with an increase in the time of application of a reverse voltage U _z =400 V (2.5-fold reduction). Fiz. Tekh. Poluprovodn. 33, 716–718 (June 1999)     

Performance evaluation of high-power GaAs Schottky and siliconp-i-n rectifiers in hard- and soft-switching applications

The dynamic switching characteristics of high-power GaAs Schottky and silicon p-i-n rectifiers are studied at various temperatures. Devices were first characterized to measure forward and reverse I-V, C-V, reverse breakdown voltage, and reverse-recovery performance. The same devices were characterized for turn on and turn off in switching circuits designed to study the dynamic switching performances under hard- and soft-switching conditions at different temperatures. Advanced two-dimensional (2-D) mixed device and circuit simulations were used to study the internal plasma dynamics under boundary conditions imposed by the circuit operation. It is shown that for hard-switching applications, GaAs Schottky power rectifiers exhibit significantly reduced switching power losses compared to silicon p-i-n rectifiers. For soft-switching applications, there is not a significant difference in the switching power losses for these two devices. Diode performance at elevated temperatures is measured and simulated, and temperature dependencies of switching and conduction power losses are analyzed     

Determining the effectiveness of HBT emitter ledge passivation byusing an on-ledge Schottky diode potentiometer

A Schottky diode, which contacts the emitter ledge directly, is used as a potentiometer to monitor the effectiveness of the emitter/base junction passivation in GaAs based heterojunction bipolar transistors (HBTs). The function and mechanism of this on-ledge potentiometer are carefully analyzed and modeled. With this apparatus, the emitter ledge potential (V_Ledge) can be measured as a function of the base-emitter bias voltage V_BE. By relating V_Ledge to V_BE. We are capable of quantifying the extent of the ledge depletion down to a few angstroms (<10 Å) in precision. The excellent detectivity of the potentiometer makes it a very powerful tool in the diagnosis of HBT problems in both operation and long-term reliability. These problems have not been detectable or distinguishable with prior techniques     

Characterization of erbium-silicided Schottky diode junction

Trap density, lifetime, and the Schottky barrier height of erbium-silicided Schottky diode are evaluated using equivalent circuit method. The extracted trap density, lifetime, and Schottky barrier height for hole are determined as 1.5/spl times/10/sup 13/ traps/cm/sup 2/, 3.75 ms and 0.76 eV, respectively. By using the developed method, the interface of the Schottky diode can be evaluated quantitatively.     

Electrical characteristics of GaAs MIS Schottky diodes

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of GaAs metal-insulator-semiconductor (MIS) Schottky barrier diodes are investigated over a wide temperature range and compared with MS diodes. The effects of the insulating layer on barrier height and carrier transport are delineated by an activation energy analysis. Excess currents observed at low forward and reverse bias have also been analyzed and their cause identified. A capacitance anomaly consistently noticed in MIS Schottky barriers is resolved by stipulating a non-uniform interfacial layer, and a self-consistent model of the GaAs MIS Schottky barrier is developed by analyzing I-V and C-V data of both MIS and MS diodes.     

Numerical analysis of GaAs epitaxial-layer Schottky diodes

A computer simulation of GaAs epitaxial-layer Schottky-barrier diodes has been carried out. The present work extends previous drift-diffusion equation (DDE) Schottky-barrier diode simulations to very thin epilayers of GaAs as well as to higher forward bias voltages. Diodes having epitaxial layers of 0.12 and 1.0 µm were modeled with an emphasis on comparison with experiment. To achieve better agreement with experimental data an interfacial layer was included in the model, resulting in a voltage-dependent barrier height. The bias voltage at which the I-V characteristic becomes strongly nonideal is predicted to depend more on the potential drop across the interfacial layer than on the series resistances present in the devices studied. The separate contributions of the dynamic resistance of the junction and of the series resistances of the epitaxial and bulk regions to the total resistance were examined for forward biases up to 1.1 V.     

硫钝化GaAs MESFET的机理研究

研究了硫钝化对GaAs MESFET直流特性的影响,并通过对钝化前后击穿电压的分析,认为负电荷表面态的增加减弱了栅靠漏一侧的电场强度,是导致器件击穿电压升高的原因.     

Experimental optimization of solar cells edge junction passivation

We have developed in this study a simple procedure to determine the optimal etching time to passivate the parasitic edge junction of solar cells. The principle of the technique is based on the control of cells electrical characteristics evolution during the gradual elimination of this edge junction. Using plasma technique, the experiments were conducted on monocrystalline and multicrystalline 4 in silicon solar cells round and square in shape respectively. For monocrystalline silicon, the edge junction etch rates of 55.5 nm/min and 90.0–96.5 nm/min has been found for a batch of 20 cells with chemically phosphorus silica glass (PSG) etched and non-etched respectively. The deduced selectivity S=Si/PSG is about 10. For a batch of 100 multicrystalline silicon solar cells, 34 min were sufficient to remove 0.4 μm parasitic junction depth. For the three batches, the difference between the etch rates is explained by the phosphorus concentration and silicon loading effect. As well as for etching uniformities, they are considered good to acceptable.     

Excess capacitance and non-ideal Schottky barriers on GaAs

Non-ideal $\text{1}\text{C}{}^2$ vs V plots showing curvature concave downwards can be transformed into linear $\text{1}\text{(C ? C}{}_0\text{)}{}^2$ vs V plots by determining the excess capacitance, C₀, as the intercept of a C vs $\text{(V + V}{}_{\mathrm{d}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ plot, where V_d is the diffusion potential. The corrected curves indicate a uniform doping profile in agreement with independent Van der Pauw measurements. An analysis of the possible significance of C₀ indicates that its value can be used as an approximate quality index for materials fabricated by different methods.     

Hydrogen passivation of defects and impurities in GaAs and InP

Hydrogen passivation experiments in GaAs and InP are discussed. For GaAs it is argued that the results of hydrogen passivation of shallow donors, shallow acceptors and deep centers in materials with different Fermi level positions as well as diffusion data for undoped or lightly doped GaAs are consistent with the assumption that hydrogen is neutral or amphoteric (at least at rather high temperatures of treatment). Some new interesting effects are reported such as improvement of GaAs homogeneity as revealed by microcathodoluminescence imaging and also hydrogen passivation of surface states in GaAs. Evidence is presented that hydrogenation in direct plasmas leads to damage region formation at the surface of the GaAs. A new method of hydrogenation is described that is free from that drawback. The marked improvement of Au/n-GaAs Schottky diodes I-V characteristics is reported after using this method. This new technique is also used to hydrogenate InP for which conventional methods encounter very serious problems. In InP the results of hydrogen passivation experiments on shallow donors and acceptors imply that hydrogen is a deep donor. An interesting effect of injection annealing at room temperature of hydrogen-donor complexes inn-InP is observed.     

钨硅化物砷化镓Schottky接触的形成和特性

本文报道了钨硅化物-砷化镓Schottky接触的形成过程和电学特性.实验表明,WSi_x/GaAs Schottky接触具有优越的I-V特性,势垒高度保持在0.8V,理想性因子实际上保持在1,并具有高温稳定性.研究表明,除了硅化物的成份,表面处理工艺和硅化物淀积技术也将对Schottky接触的I-V特性和热稳定性产生强烈的影响.本文提出利用对GaAs衬底的溅射腐蚀和在淀积过程中加以负的衬底偏置能显著地改进金属层与衬底的粘附性.     

GaAs MESFET肖特基结参数表征及其应用

运用双指数函数模型方法分析了影响GaAsMESFET肖特基势垒结特性的各种因素 ,编制了结参数提取和I -V曲线拟合软件 ,实现了通过栅源正向I-V实验数据提取反映肖特基势垒结特性的 6个结参数 ,其结果与实验数据吻合得很好。并对TiAl栅和TiPtAu栅GaAsMESFET进行了高温储存试验前后的结参数对比分析和深能级瞬态谱 (DLTS)验证分析 ,证明这种结参数表征方法是进行器件特性、参数的稳定性与退化和肖特基势垒结质量研究的一种新的实用可行的分析手段。     

Measurement of Richardson constant of GaAs Schottky barriers

The Richardson constants for near-ideal AuGaAs and AlGaAs Schottky diodes have been determined from an analysis of forward current-voltage characteristics. Measurement of capacitance-voltage characteristics at different temperatures shows that the barrier heights of the diodes have very similar temperature dependence for both Au and Al contacts. On taking into account the temperature dependence of the barrier height, the corrected value of the Richardson constant for AuGaAs diode is found to be very close to the predicted theoretical value. The corresponding value for AlGaAs diode is about a factor of five smaller which is explained on the basis of a thin interfacial layer between Al and GaAs.     

双面Schottky势垒型GaAs粒子探测器特性

双面肖特基势垒型 Ga As粒子探测器由半绝缘砷化镓材料制成 ,器件结构为金属 -半导体-金属结构 ,该探测器能经受能量为 1 .5Me V、剂量高达 1 0 0 0 k Gy的电子、50 0 k Gy的 γ射线、β粒子、X射线等粒子的辐照测试 ,辐照后器件击穿曲线坚挺 ,反向漏电流最低为 0 .48μA.器件的另一特征是其反向漏电流与 X射线的照射量呈线性关系 .该探测器在 2 4 1Am( Eα=5.48Me V) α粒子辐照下 ,其最大的电荷收集率和能量分辩率分别为 45%和 7% .在由 90 Sr( Eβ=2 .2 7Me V)发出的 β粒子辐照下 ,探测器有最小的电离粒子谱 .该探测器对光照也有明显的响应