高峰谷电流比的高掺杂发射区In0.53Ga0.47As/AlAs共振隧穿二极管

利用空气桥工艺设计和制作了高掺杂发射区In0.53Ga0.47As/AlAs共振隧穿二极管（RTD）。在室温下,器件的峰谷电流比大于40,峰值电流密度为24kA/cm2。建立了RTD器件等效电路模型,并从直流和微波测试结果中提取出器件参数。高峰谷电流比的RTD器件具有非常小的电容,有利于在微波/太赫兹领域中的应用。     

Reliability investigation of InGaP/GaAs HBTs under current and temperature stress

The reliability of InGaP/GaAs N–p–n heterojunction bipolar transistors (HBTs) with different base metal contact systems (Au/Zn/Au, Ti/Au, Ti/Pt/Au and the novel Ti/ZrB₂/Au) under current and temperature stress is studied in this paper. We further report results of current stress on three p-GaAs doping impurities namely Zn, Be and C. The effect of O⁺/H⁺ and O⁺/He⁺ ions, used in the fabrication of planar self-aligned HBTs, is also investigated in the stability of device dc current gain. The instability phenomena typical of each factors and their effects on the HBT characteristics are reported.     

Au and non-Au based rare earth metal-silicide ohmic contacts to p-InGaAs

The aim of this study is to improve the electrical properties of ohmic contacts that plays crucial role on the performance of optoelectronic devices such as laser diodes (LDs), light emitting diodes (LEDs) and photodetectors (PDs). The conventional (Pd/Ir/Au, Ti/Pt/Au and Pt/Ti/Pt/Au), Au and non-Au based rare earth metal-silicide ohmic contacts (Gd/Si/Ti/Au, Gd/Si/Pt/Au and Gd/Si/Pt) to p-InGaAs were investigated and compared each other. To calculate the specific contact resistivities the Transmission Line Model (TLM) was used. Minimum specific contact resistivity of the conventional contacts was found as 0.111 × 10⁻⁶ Ω cm² for Pt/Ti/Pt/Au contact at 400 °C annealing temperature. For the rare earth metal-silicide ohmic contacts, the non-Au based Gd/Si/Pt has the minimum value of 4.410 × 10⁻⁶ Ω cm² at 300 °C annealing temperature. As a result, non-Au based Gd/Si/Pt contact shows the best ohmic contact behavior at a relatively low annealing temperature among the rare earth metal-silicide ohmic contacts. Although the Au based conventional ohmic contacts are thermally stable and have lower noise in electronic circuits, by using the non-Au based rare earth metal-silicide ohmic contacts may overcome the problems of Au-based ohmic contacts such as higher cost, poorer reliability, weaker thermal stability, and the device degradation due to relatively higher alloying temperatures. To the best of our knowledge, the Au and non-Au based rare earth metal-silicide (GdSi_x) ohmic contacts to p-InGaAs have been proposed for the first time.     

Low resistance, thermally stable Au/Pt/Ti/WSiN ohmic contacts on n+-InGaAs/n-GaAs layer systems

The electrical properties of the ohmic contact systems Au/Pt/Ti/WSiN and Au/Pt/Ti to n⁺-InGaAs/GaAs layers grown by metalorganic vapor phase epitaxy were investigated and compared to each other. The thermal stability properties of these contact systems were characterized by accelerated stress tests at elevated temperatures and by complementary thin film x-ray diffraction analysis to evaluate the microstructural properties of degraded and nondegraded structures. The goal of these efforts was to develop stable, homogeneous emitter contacts for power heterojunction bipolar transistors. It was found that for both contact systems the best (specific) contact resistance R_c (ρ _c) is about 0.05 Ωmm (2 × 10⁻⁷ Ωcm²) in the as-deposited state. Au/Pt/Ti/WSiN contacts show no degradation after aging at 400°C for more than 20 h. This is in contrast to standard Au/Pt/Ti contacts which significantly degrade even after short time annealing at 400°C. The good long-time stability of the Au/Pt/Ti/WSiN system is related to the advantageous properties of the reactively sputtered WSiN barrier layer.     

Metallurgical stability of ohmic contacts on thin baseInP/InGaAs/InP HBT's

The metallurgical stability of ohmic contacts: Pt, Pt/Ti, Au/Ti, Au/Pt/Ti, and Au/Pt/Ti/W, on a 500 Å thick p⁺-InGaAs base of InP/InGaAs/InP HBTs have been investigated as a function of anneal temperature. All contacts were stable after a 300°C-30 s anneal. Pt contact failed at 350°C whereas Pt/Ti, Au/Ti, and Au/Pt/Ti contacts failed at 400°C. The failure mechanism was a collector leakage short owing to the penetration of Pt or Ti through the thin base. Only HBTs with Au/Pt/Ti/W contact were still functional after a 400°C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions     

Emitter-metal-related degradation in InP-based HBTs operating at high current density and its suppression by refractory metal

We investigated the reliability of InP-based HBTs with a ledge structure, focusing on emitter-metal-diffusion-induced degradation. Bias-temperature accelerated tests under high temperatures and high current densities of up to 5 mA/μm² were conducted for HBTs with conventional emitter electrodes, whose metal configuration was Ti/Pt/Au, and for HBTs with refractory metal emitters of Ti/Mo-Ti/Pt/Au, Ti/W-Ti/Pt/Au, or W-Ti/Pt/Au. The emitter contact layer was analyzed by transmission electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron diffraction. Severe damage and disruption of uniformity of the atomic composition were observed due to diffusion of Ti and Au in HBTs with conventional emitter, whereas suppression of those degradations was observed in HBTs with refractory emitter. Refractory metals were found to be advantageous for blocking upper metal diffusion. Interstitials of host species generated due to metal diffusion must cause a shift of atomic composition.The time-wise change in the emitter resistance was estimated to compare the speed of the contact layer degradation between different emitter electrode metals. The critical time, which we determined as an emitter resistance increases of 3% from the initial value, increased by one order for HBTs with refractory metal than for HBTs with conventional metal at the same junction temperature, despite the same activation energy of 2.0 and 1.65 eV for J_c of 2 and 5 mA/μm², respectively, for all types of emitter electrode. The advantages of refractory metal for improving the reliability of InP HBTs were confirmed, especially for operation at high current densities.     

1.0μm栅长GaAs基MHEMT器件及SPDT开关MMIC

利用MBE外延材料和接触式光学光刻方式,成功制备出1.0μm栅长GaAs基MHEMT器件,分别蒸发Pt/Ti/Pt/Au和Ti/Pt/Au作为栅电极金属.获得了优越的DC和RF性能,Pt/Ti/Pt/Au和Ti/Pt/Au MHEMT器件的gm为502(503)mS/mm,JDss为382(530)mA/mm,VT为0.1(-0.5)V,fT和fmax分别为13.4(14.8),17.0(17.5)GHz.利用单片集成增强/耗尽型GaAs基MHEMT器件制备出九阶环型振荡器,直流电压为1.2V时,振荡频率达到777.6MHz,门延迟时间为71.4ps.利用Ti/Pt/Au MHEMT器件设计并制备出了DC-100Hz单刀双掷(SPDT)关MMIC,其插入损耗、隔离度、输入输出回波损耗分别优于2.93,23.34和20dB.     

退火参数对p型GaAs欧姆接触性能的影响

采用磁控溅射的方法在p型GaAs衬底上沉积了Ti/Pt/Au金属薄膜,研究了退火工艺参数(温度和时间)对p-GaAs/Ti/Pt/Au欧姆接触性能的影响。结果表明:p-GaAs上制作的Ti/Pt/Au金属系统能在很短的退火时间(60 s)内形成很好的欧姆接触。过分延长退火时间,并不能改善系统的欧姆接触性能。退火温度在400~450℃时均可得到较好的欧姆接触。当退火温度为420℃,退火时间为120 s时,比接触电阻率达到最低,为1.41×10–6.cm2。     

Room-Temperature Oscillation of Resonant Tunneling Diodes close to 2 THz and Their Functions for Various Applications

Compact and coherent source is a key component for various applications of the terahertz (THz) wave. We report on our recent results of THz oscillators using resonant tunneling diodes (RTDs). To achieve high-frequency oscillation, the electron delay time of RTD was reduced with a narrow quantum well and an optimized collector spacer thickness. Conduction loss at the air bridge connecting RTD and slot antenna, which works as a resonator and a radiator, was also reduced. By these structures, a fundamental oscillation up to 1.92 THz was obtained at room temperature. Theoretical calculation shows that an oscillation over 2 THz is further expected by improved structures of RTD and antenna. Using the offset slot antenna and two-element array configuration, high output power of 0.61 mW was obtained at 620 GHz. A direct intensity modulation of RTD oscillators up to 30 GHz, which is useful for high-speed wireless data transmission, was demonstrated. By the integration of a varactor diode, wide frequency sweep of 580–700 GHz in a single device and 580–900 GHz in a four-element array were also demonstrated. This result expands possible applications of RTD oscillators.     

Effect of Pt barrier on thermal stability of Ti/Al/Pt/Au in ohmic contact with Si-implanted n-type GaN layers

We report the effect of the Pt barrier on the thermal stability of Ti/Al/Pt/Au in ohmic contact with Si-implanted n-type GaN layers. Ti/Al/Au (25/100/200 nm) and Ti/Al/Pt/Au (25/100/50/200 nm) multilayers were, respectively, deposited on as-implanted and recovered Si-implanted n-type GaN samples. The associated dependence of the specific contact resistance on the annealing time at various temperatures was compared. The long-term ohmic stability of a Ti/Al/Pt/Au multilayer in contact with a Si-implanted n-type GaN layer was much better than that of the Ti/Al/Au multilayer. This superior stability is attributed to the barrier function of the Pt interlayer. The Pt/Au bilayer can also passivate the propensity of oxidation for the conventional Ti/Al bilayer in contact with n-type GaN layers at elevated temperatures.     

AlGaN/GaN HEMT器件的研制

介绍了AlGaN/GaNHEMT器件的研制及室温下器件特性的测试.漏源欧姆接触采用Ti/Al/Pt/Au ,肖特基结金属为Pt/Au .器件栅长为1μm ,获得的最大跨导为12 0mS/mm ,最大的漏源饱和电流密度为0 95A/mm .     

Effect of Cryogenic Temperature Deposition of Various Metal Contacts on Bulk Single-Crystal <Emphasis Type="Italic">n</Emphasis>-Type ZnO

The effect of cryogenic temperatures during metal deposition on the contact properties of Pd, Pt, Ti, and Ni on bulk single-crystal n-type ZnO has been investigated. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. By sharp contrast, both Pd and Pt contacts showed rectifying characteristics after deposition with barrier heights between 0.37 eV and 0.69 eV. Changes in contact behavior were measured on Pd to anneal temperatures of ∼300 °C, showing an increase in barrier height along with a decrease in ideality factor with increasing annealing temperature. This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no differences in near-surface stoichiometry for the different deposition temperatures; however, low temperature contacts demonstrated some peeling/cracking for Pt and Pd.     

Nanomeshed Pt(Au) Transparent Contact to p-GaN of Light-Emitting Diode

This study examines nanomeshed Pt and Pt(Au) thin films formed by a dewetting process on a p-GaN surface. With prolonged annealing, the Pt(Au) layer shows more stable contact resistance to p-GaN and lower sheet resistance than the Pt layer. L–I curves show that the GaN light-emitting diode (LED) with the Pt(Au) transparent conducting layer (TCL) produces more light output power than the GaN LED with the Pt TCL. The higher light output of the LED with the Pt(Au) TCL is attributed to the lower sheet resistance, which improves current spreading in the active region.     

The thermal stability of ohmic contact to n-type InGaAs layer

The thermal stability of ohmic contact to n-type InGaAs layer is investigated. When Ni/Ge/Au is used as the contact metal, the characteristics of the ohmic contact are degraded after thermal treatment. The specific contact resistance of (Ni/Ge/Au)-InGaAs ohmic contact after annealing at 450°C is about 15 times larger than that of as-deposited sample. This is due to the decomposition of InGaAs and the interdiffusion of Ga and Au. A new phase of Au₄ln appears after annealing at 300°C. While in the case of Ti/Pt/Au, Au does not penetrate into the InGaAs layer as revealed by secondary ion mass spectroscopy. The specific contact resistance of (Ti/Pt/Au)-InGaAs ohmic contact after annealing at 450°C is eight times larger than that of as-deposited sample. Therefore, the thermal stability of (Ti/Pt/Au)-InGaAs ohmic contact is better than that of (Ni/Ge/Au)InGaAs ohmic contact.     

High thermal stability AlGaAs/InGaAs enhancement-mode pHEMT using palladium-gate technology

The dc, flicker noise, power, and temperature dependence of AlGaAs/InGaAs enhancement-mode pseudomorphic high electron mobility transistors (E-pHEMTs) were investigated using palladium (Pd)-gate technology. Although the conventional platinum (Pt)-buried gate has a high metal work function, which is beneficial for increasing the Schottky barrier height of the E-pHEMT, the high rate of intermixing of the Pt-GaAs interface owing to the effect of the continuous production of PtAs₂ on the device influenced the threshold voltage (V_th) and transconductance (g_m) at high temperatures or over the long-term operation. Variations in these parameters make Pt-gate E-pHEMT-related circuits impractical. Furthermore, a PtAs₂ interlayer caused a serious gate leakage current and unstable Schottky barrier height. This study presents the Pd-GaAs Schottky contact because Pd, an inert material with high work function of 5.12 eV. Stable Pd inhibited the less diffusion at high temperatures and simultaneously suppressed device flicker noise. The V_th of Pd/Ti/Au Schottky gate E-pHEMT was 0.183 V and this value shifted to 0.296 V after annealing at 200 °C. However, the V_th shifted from 0.084 to 0.231 V after annealing of the Pt/Ti/Au Schottky gate E-pHEMT because the Pt sunk into a deeper channel. The slope of the curve of power gain cutoff frequency (f_max) as a function of temperature was −5.76 × 10⁻² GHz/°C for a Pd/Ti/Au-gate E-pHEMT; it was −9.17 × 10⁻² GHz/°C for a Pt/Ti/Au-gate E-pHEMT. The slight variation in the dc and radio-frequency characteristics of the Pd/Ti/Au-gate E-pHEMT at temperatures from 0 to 100 °C revealed that the Pd-GaAs interface has great potential for high power transistors.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

P型GaAs欧姆接触的制作

在以Be作为离子源离子注入形成的P型GaAs衬底上分别使用Ti/Pt/Au和Cr/Pt/Au多层金属作为欧姆接触金属,并对比合金前后的差别。结果表明,使用Ti/Pt/Au作为欧姆接触金属效果更好,合金对于降低欧姆接触电阻率效果明显,合金后Ti/Pt/Au的接触电阻率可达到3.08×10-5Ω.cm2。     

High-temperature aging tests on planar structure InGaAs/InP PIN photodiodes with Ti/Pt and Ti/Au contact

Planar structure InGaAs/InP PIN photodiodes having low dark current and low junction capacitance characteristics were reproducibly fabricated by using VPE wafers. Bias/temperature life testings for the diodes showed that there were no significant degradations after 5500 h aging at 250°C and 10 V reverse bias by adopting the Ti/Pt and Ti/Au metals for the p-side contact.     

Study on the failure temperature of Ti/Pt/Au and Pt5Si2-Ti/Pt/Au metallization systems

The Ti/Pt/Au metallization system has an advantage of resisting KOH or TMAH solution etching. To form a good ohmic contact, the Ti/Pt/Au metallization system must be alloyed at 400℃. However, the process temperatures of typical MEMS packaging technologies, such as anodic bonding, glass solder bonding and eutectic bonding, generally exceed 400℃. It is puzzling if the Ti/Pt/Au system is destroyed during the subsequent packaging process. In the present work, the resistance of doped polysilicon resistors contacted by the Ti/Pt/Au metallization system that have undergone different temperatures and time are measured. The experimental results show that the ohmic contacts will be destroyed if heated to 500℃. But if a 20 nm Pt film is sputtered on heavily doped polysilicon and alloyed at 700℃ before sputtering Ti/Pt/Au films, the Pt₅Si₂-Ti/Pt/Au metallization system has a higher service temperature of 500℃, which exceeds process temperatures of most typical MEMS packaging technologies.     

Degradation mechanism of GaAs MESFETs

The reliability of the Au/Pt/Ti Schottky gate of low-high doped GaAs MESFETs has been investigated by thermal step stress and accelerated life tests and their degradation mechanisms were analyzed by means of Auger electron spectroscopy, X-ray diffractometry, cross-sectional transmission electron microscopy, current-voltage, and capacitance-voltage measurements. Electrical measurements showed that the failure of the GaAs MESFETs was mainly due to the degradation of the Au/Pt/Ti/GaAs Schottky contact. An activation energy of 1.3 eV and a lifetime of 2 × 10⁸ h at 125°C for Schottky contact were evaluated. At a temperature lower than 350°C, the degradation of the Schottky contact is attributed to the decrease of net electron concentration caused by outdiffusion of host Ga atoms of GaAs. The activation energy for the decrease of net electron concentration is determined to be 1.4 eV using the capacitance-voltage measurement, which is consistent with 1.3 eV obtained by the accelerated life tests. This suggests that the major thermal degradation mechanism at a temperature lower than 350°C is the outdiffusion of Ga atoms from the channel. Meanwhile, the effective channel thickness at a temperature higher than 350°C is reduced by the formation of TiAs at the Schottky interface, the activation energy of which is determined to be 1.74 eV.