用激光形成Ⅲ—V族化合物半导体的欧姆接触

本文报导了采用聚焦激光束在Ⅲ—Ⅴ族化合物半导体表面上形成欧姆接触。我们利用脉冲红宝石激光器(λ=0.6943微米),脉冲钇铝石榴石激光器(λ=1.06微米)和Q-开关CO_2激光器(λ=10.6微米)的脉冲群,已在几种Ⅲ—Ⅴ族化合物(Gap,GaAs,GaSb,InAs和InSb)上形成了“欧姆”接触。初步结果表明,只有波长落在半导体吸收带内(自由载流子吸收或带到带跃迁区)的那些激光器能够成功地用于这种目的。用这种方法制作的接触所给出的欧姆特性类似于用常规技术得到的特性。用这种方法制备欧姆接触不需要任何特殊的表面制备,而且,因为加热被限制在局部的表面区,因此,它对器件的结特性没有影响。     

用脉冲激光束在N型GaAs上制备欧姆接触

本文用调Q红宝石脉冲激光器(波长6943A、脉宽30ns)以1.1～2.9J/cm~2的激光能量密度,在N型GaAs上进行激光合金化研究,试验了不同GaAs外延层浓度、不同合金层组分、不同激光脉冲次数对欧姆接触电阻率的影响。结果表明,适当能量密度激光合金化所得到的接触电阻率同加热合金化最好结果相当或更好,激光合金化表面均匀,质量好,而且不影响半导体器件内结的特性。     

激光束制备砷化镓欧姆接触的实验研究

本实验使用Q开关Nd∶YAG激光器产生脉冲激光束处理n型GaAs外延片上蒸发的纯Ge膜,取得了良好的欧姆接触,特征接触电阻率最佳值可达1×10~(-6)欧·厘米~2。本文描述了这项实验研究的简单内容,并且指出以激光合金Ge膜制备n型GaAs欧姆接触的方法用于GaAs器件和集成电路制作工艺中的可能性。     

用连续CO_2激光合金化制备Au-Ge-Ni-n GaAs欧姆接触

本文利用CW CO_2激光对GaAs的穿透性从GaAs晶片背面进行辐照,形成了良好的Au-Ge-Ni-n GaAs欧姆接触。研究了激光合金化对不同摻杂浓度GaAs的欧姆接触,并与热合金化作了对比试验。结果表明,激光合金化有较低的比接触电阻,材料的载流子浓度越低,比接触电阻降低得越显著。AES分析表明,激光合金化造成了一个优良的以Ge取代Ga的重掺杂的n型GaAs层。     

注Z_n~ -GaAs的激光退火及GaAs欧姆接触的激光合金化

本文研究了激光退火使离子注Zn的GaAs层获得高的表面浓度作P~ 层.所用的调Q红宝石激光器能量密度1～1.5J/cm~2、脉宽20ns.霍尔测量得到的表面空穴浓度达3.3 × 10~(19)-8.7 ×10~(20)/cm~3,红外等离子共振极小测量结果与之相符.电子衍射实验观察到注入无定形层经激光退火后再结晶的单晶衍射花样. 另外,也报道了用激光合金化在N型和P型体GaAs材料上制备欧姆接触的结果,所得到的比接触电阻比通常热合金化的比接触电阻略低,其表面形貌也比热合金化的好.     

注Z_n~+-GaAs的激光退火及GaAs欧姆接触的激光合金化

本文研究了激光退火使离子注Zn的GaAs层获得高的表面浓度作P~+层.所用的调Q红宝石激光器能量密度1～1.5J/cm~2、脉宽20ns.霍尔测量得到的表面空穴浓度达3.3 × 10~(19)-8.7 ×10~(20)/cm~3,红外等离子共振极小测量结果与之相符.电子衍射实验观察到注入无定形层经激光退火后再结晶的单晶衍射花样. 另外,也报道了用激光合金化在N型和P型体GaAs材料上制备欧姆接触的结果,所得到的比接触电阻比通常热合金化的比接触电阻略低,其表面形貌也比热合金化的好.     

非共晶Au/Ge欧姆接触工艺改善扩散法n沟道GaAs MESFET

用非共晶组份Au/Ge合金做n型GaAs欧姆接触.系统测定了不同Au,Ge厚度做欧姆接触的比接触电阻值.以150A|°Ge/2000—2500A|°Au的配比,在400℃,10min(实际是3min)下合金化,其比接触电阻值能与文献报道的数据相比较,且表面很平.这有利于栅长≤1μm场效应管的光刻,且能改进器件性能与成品率.用作在高阻衬底上以扩散法制备n沟道场效应管的欧姆接触,改进的器件性能在栅长是1.2μm,栅宽150μm时,跨导8m达29m3.另一个样品在栅长1.3μm,栅宽300μm时,fmax=21GHz,在4GHz下,噪声系数N_F≤1.5dB,相关增益Gα为11dB.     

难熔金属与n-GaAs的欧姆接触特性

用磁控溅射系统和快速合金化法制备了Mo/W/Ti/Au多层金属和n-GaAs材料的欧姆接触,在溅射金属层之前分别用HCl溶液和(NH4)2S溶液对n-GaAs材料的表面进行处理.用传输线法对比接触电阻进行了测试,并利用俄歇电子能谱(AES)、X射线衍射图谱(XRD)对接触的微观结构进行了分析.结果表明,用(NH4)2S溶液对n-GaAs材料表面进行处理后,比接触电阻最小;在700℃快速合金化后获得最低的比接触电阻,约为4.5×10-6Ω·cm2.这是由于(NH4)2S溶液钝化处理后降低了GaAs的表面态密度,消除了费米能级钉扎效应,从而改善了难熔金属与GaAs的接触特性.     

Analysis of Damage Induced by Repetition-Frequency Optical Pulse in Semi-insulating GaAs PCSS's Material

通过波长为1064 nm的重频激光光脉冲触发半绝缘GaAs光导开关损伤测试实验,观察脉冲激光触发过程中光电导开关电阻率的变化,对比低重频(＜1 kHz)和高重频的激光脉冲对GaAs光电导开关芯片的损伤阈值,分析了不同重复频率的激光脉冲引起光导开关芯片材料光损伤的主要原因,并探讨了损伤机理.研究表明,在重复频率激光作用下GaAs光导开关芯片材料的破坏阈值比在单脉冲作用下低,且不同重复频率的激光辐照下材料表面的温升速率不同.当激励光脉冲重复频率较低(＜1 kHz)时,芯片内的温升效应不显著,此时光损伤与重复频率无明显依赖关系,主要损伤机制为微损伤累积;而当重复频率较高时,开关材料内热积累引起的损伤占主要地位.     

激光扩散锡实现n-GaAs层上的非合金欧姆接触

澳大利亚科学家最近报导了一种新的扩散技术,在 GaAs 材料上实现非合金欧姆接触。把一种掺杂感光乳胶膜复在 GaAs 片上,用脉冲激光照射,制得掺锡的 n~ 型 GaAs 层,然后在其上实现非合金欧姆接触。这是一种浅层杂质扩散技术,用于 GaAs 金属半导体场效应器件的制备。但热扩散难以得到低阻的非合金欧姆接触,而连续激光又不能独立完成扩散过程,因此,作者使用红宝石脉     

Formation of ohmic contacts to III–V semiconductors,using a laser beam

This paper reports on the use of a focused laser beam to form ohmic contacts on the surfaces of III–V semiconductors. We have produced “ohmic” contacts on several III–V compounds (GaP, GaAs, GaSb, InAs and InSb) using a pulsed ruby laser (λ = 0·6943 μm), a pulsed YAG laser (λ = 1·06 μm) and a burst of pulses from a Q-switched CO₂ (λ = 10·6 μm) laser. The initial results show that only those lasers whose wavelengths fall within the absorption band of the semiconductor (free carrier absorption or band to band transition region) can be successfully used for this purpose. Contacts produced in this manner show ohmic characteristics similar to that obtained with conventional techniques. The method does not require any special surface preparation, and since the heating is limited to a localized surface region it has no effect on the junction properties of a device.     

Ohmic contacts on n-GaAs produced by spark alloying

A new method of forming ohmic contacts on n-GaAs using electroplated Sn/Au and alloying with a high frequency spark generator is described. This process gives an average contact resistance of 3.9×10?6±0.2×10?6 ?cm2, which is comparable to results obtained by laser irradiation and indirect electric heating. The sparking technique produces uniform alloying of the substrate surface, while avoiding high temperatures throughout the substrate.     

Selective formation of ohmic contacts to n-GaAs

A new process is presented for ohmic contact realisation to n-GaAs. The process enables selective formation of ohmic contacts showing ohmic characteristics without an alloying process. This is realised through the deposition of a heavily doped n-Ge layer on an n-GaAs layer. It is possible to grow a Ge layer on GaAs without deposition on SiO2 which is used as a mask. A Ge layer with doping in excess of 1019 cm?3 can be obtined, using GeH4, PH3 and H2 as source gases. This doping level is sufficiently high to exhibit nonalloyed ohmic characteristics.     

Low-resistance vertical conduction across epitaxially lifted-off n-GaAs film and Pd/Ge/Pd coated Si substrate

Low-resistance ohmic conduction across an epitaxially lifted-off (ELO) thin n-GaAs film and a Si substrate was obtained by attaching the ELO film on the Si substrate coated with a Pd/Ge/Pd multilayer. Good bonding and ohmic contacts to both GaAs and Si were achieved at the same time after annealing. The interface compound formation was studied by secondary ion mass spectroscopy and x-ray diffraction analyses. The ELO technology was used to fabricate an ELO stripe geometry diode laser on Si with the back-side contact on Si substrate. Good laser performance with comparable characteristics as conventional laser diodes on GaAs substrates was obtained.     

HEMT with nonalloyed ohmic contacts using n+-InGaAs cap layer

We have investigated nonalloyed ohmic contacts on HEMT's using a highly conductive n⁺-InGaAs layer. The minimum specific contact resistance obtained was 4.8 × 10^-7Ω.cm², and the IV characteristics were equal to or better than those of conventional HEMT's with alloyed ohmic contacts. The maximum transconductances of a nonalloyed ohmic HEMT were 240 mS/mm at 300K and 340 mS/mm at 88K for a gate length of 1.1 µm. We conclude that it is not necessary for HEMT's with two-dimensional electron gas (2DEG) channels to have alloyed ohmic contacts, because the tunneling conduction is significant at the n-GaAs/n-AlGaAs/undoped GaAs double heterojunction.     

Laser annealed Ta/Ge and Ni/Ge ohmic contacts to GaAs

Refractory metal ohmic contacts to n-type GaAs have been developed using epitaxial Ge films and pulsed laser annealing. Laser annealing was carried out with a 22 ns pulse from a Q-switched ruby laser operating in the TEM00mode. The specific contact resistivity of the contacts Ta/Ge and Ni/Ge on 2 × 10¹⁷cm^-3dopes GaAs exhibited sharp minima as a function of laser energy density at 1 × 10^-6Ω-cm²and 2 × 10^-6Ω-cm², respectively, which occurred near the melting point of the layered contacts. Auger electron sputter profiles revealed Ge migration into the GaAs surface after laser annealing at sufficient energy density to form ohmic contact. The contacts have applications to high temperature devices and to devices which experience high channel or contact temperatures, such as power FETs and TEDs.     

Development of InxGa1−xAs-based ohmic contacts for p-type GaAs by radio-frequency sputtering

In_xGa_1−xAs-based ohmic contacts which showed excellent contact properties for n-GaAs were demonstrated to be applicable to p-GaAs ohmic contacts. These contacts, prepared by radio-frequency sputtering, provided low contact resistance (0.2 Ω-mm), excellent thermal stability, smooth surface, and good reproducibility. The contact resistances had a weak dependence on the annealing temperatures, which was desirable in a manufacturing view point. This weak temperature dependence was explained to be due to a unique Schottky barrier height at the metal/p-In_xGa_1−xAs interface which does not depend on the In concentration in the In_xGa_1−xAs layer. The present experiment showed the possibility of simultaneous preparation of ohmic contacts for both n and p-GaAs using the same contact materials.     

Sintered ohmic contacts to n-and p-type GaAs

Previously, all known ohmic contacts to n-GaAs have involved a so-called "alloying" procedure which consists of melting a Au-Ge eutectic or Sn-based alloy films on GaAs. We describe here a new contact metallization scheme consisting of Pd/Ge/n-GaAs which requires sintering rather than melting in order to produce ohmic contacts. The sintering is done at temperatures ranging from 350°C, 15 min to 500°C, 2 h depending on the doping level of n-GaAs (10¹⁸-10¹⁶cm^-3. For n-10¹⁶cm^-3GaAs, a specific contact resistance of 3 × 10^-4Ω.cm²was achieved. Sintering leads to the formation of some PdGe and intermetallics associated with the Pd/GaAs interaction, namely, PdAs2and PdGa. Ohmic behavior is attributed to a combination of the doping action of Ge (as donor) and fast in-diffusion kinetics of Pd. Sintered contacts to n⁺and p⁺GaAs (ND.A∼ 10¹⁸cm^-8) made by Au, Pt, and Ti Were also investigated for ohmic behavior. Each of these three metals was at least partially effective in forming ohmic contacts to p⁺GaAs; the degree of effectiveness increases on going from Ti to Au to Pt. It is proposed that a reasonable guideline to follow When searching for ohmic contacts is Xm≳ Xdwhere Xmis the width of the metallurgical junction and Xdis the ideal depletion layer width. This condition should favor ohmic contacts by promoting a micro 3-dimensional current flow at the conductor-semiconductor interface and thereby maximizing field-emission probability.     

Low resistance pd/ge ohmic contacts to epitaxially lifted-off n-type GaAs film

A low resistance PdGe nonalloyed ohmic contact has been successfully formed to epitaxially lifted-off n-type GaAs films. The contact is made by lifting off partially metallized n-type GaAs films using the epitaxial lift-off method and bonding them to metallized Si substrates by natural intermolecular Van Der Waals forces. Low temperature sintering (200°C) of this contact results in metallurgical bonding and formation of the ohmic contact. We have measured specific contact resistances of 5 × 10⁻⁵ Ω-cm₂ which is almost half the value obtained for pure Pd contacts. Germanium forms a degenerately doped heterojunction interfacial layer to GaAs. Our experimental results show that germanium diffuses to the interface and acts as a dopant layer to n-GaAs film surface. Therefore, for epitaxially lifted-off n-type GaAs films, PdGe is a low resistance ohmic metal contact to use.     

Au/Pt/AuGe/Ni中Pt扩散阻挡层对n-GaAs欧姆接触的影响

The multi-layer metals of Ni/Au Ge/Pt/Au with a Pt diffusion barrier layer of ohmic contact to n-GaAs were studied. The surface morphology and ohmic contact resistivity of multi-layer metals were characterized, with and without the Pt diffusion barrier layer for comparison. The SEM and EDS measurements show the Pt diffusion barrier layer can block the interdiffusion of atoms in multi-layer metals, and improve the surface morphology.The TLM results show that the samples with a Pt diffusion barrier layer have uniform ohmic contact resistance,indicating that the Pt diffusion barrier layer can increase the repetition and uniformity of ohmic contact to n-GaAs,and improve the thermal stability and reliability of GaAs-based devices.