The formation of furnace processed Te- and Ge-based ohmic contacts on n-GaAs was investigated using Rutherford Backscattering Spectroscopy and electrical measurements. Contact resistivities obtained with the Ni/Au/Te metallization were comparable to those of the standard Ni/AuGe scheme, the lowest value for both metallizations being 5.10−6Qcm2. The onset of ohmicity of the Au/Te scheme varied from 480°C to 550°C by changing the Au/Te thickness ratio. The diffusion characteristics of the contacting metals were studied on GaAs as well as on SiO2 substrates. Arguments in favor of the model explaining the nature of the contacts by the formation of a heterojunction-like structure are adduced.

Rapid thermal processing has been utilized to diffuse Zn into GaAs from a thin film zinc silicate source prepared by atmospheric pressure chemical vapor deposition (CVD). The zinc source was capped with ∼500 Å of silicon dioxide (SiO2 ). At 750°C for 20 sec, the diffusion of Zn reached a depth of 0.8 μm. For these diffusions, the diffusion constant is concentration dependent and is proportional to the square of the Zn concentration. Above 7500 C, anomalous secondary diffusion fronts were observed in the Zn diffusion profiles. A new model is proposed that explains the diffusion profiles at all temperatures. Ohmic contacts have been made to the above Zn-diffused surfaces using Cr/AuZn/Au metallizations. A typical value of the specific contact resistance is 8.0 × 10−7 ohm-cm2.

Control of the structure and chemistry at the interfaces of compound semiconductors is essential for the commercial use of these materials in electronic and optical technologies. This can only be achieved when the governing thermodynamics and kinetics of interfacial reactions are understood. Based primarily on the experience of metal/Si interactions, however, a prevailing belief was born that thin-film reactions follow a separate set of thermodynamic and kinetic “rules” which are different from bulk reactions. The intent of our work has been to not only characterize metal/GaAs contact reactions but also to rationalize these reactions with equilibrium phase diagrams and bulk metal/GaAs diffusion couple experiments. Through this approach, a better understanding of thin-film and bulk differences has been obtained.

The Ir/GaAs system is used as an example. Phase formation and reaction kinetics were studied for 30 nm Ir films on (100) GaAs using TEM, XTEM, and AEM. Bulk diffusion between 0.25 mm thick Ir foil and (100) GaAs wafers was studied with SEM and electron probe microanalysis (EPMA). The diffusion paths and kinetics were the same for thin-film and bulk. The phase sequence Ir/IrGa/IrAs2/GaAs formed for all diffusion couples. Reaction kinetics were parabolic with an activation energy of 3.0 eV for both thin-film and bulk, and the data was colinear in an Arrhenius plot. Reacted layer morphology in both cases was layered. The effects of grain size, crystallographic texturing, and the relative diffusivities of the components on the reaction mechanisms in bulk versus thin-film reactions are considered.

The correlation between the microstructure and phase formation, and the electrical properties for the Co/GaAs, Co/Ge/GaAs and Ge/Co/GaAs systems have been studied. The microstructural analysis was carried out by transmission electron microscopy, and the component redistribution was determined by Auger electron spectroscopy. The electrical properties (Schottky barrier height and contact resistivity) were studied by means of current-voltage and capacitance-voltage measurements.

The epitaxical and thermally stable NiAI/(AI, Ga)As system is shown to meet all of the basic materials criteria for buried metal/compound semiconductor heterostructures. We describe the growth of these heterostructures by molecular beam epitaxy. Even the thinnest buried NiAI films grown thus far (1.5 nm) are electrically continuous and metallic. Electron tunneling and lateral transport measurements provide strong evidence for size quantization in NiAl films thinner than 3.5 nm. The merging of compound semiconductor tunneling barriers with epitaxical metallic quantum wells and the ability to selectively contact buried metallic quantum wells is expected to yield novel three-terminal devices.

Films of CoGa and CoAs have been deposited on Ga1-xAlxAs surfaces. CoAs films were found to be highly textured, but not single crystal. For CoGa films, however, single crystal growth was observed. The crystalline quality of the (100) oriented CoGa was good as determined by Rutherford backscattering with channeling measurements (χmin ∼7%) and cross-sectional transmission electron microscopy. Schottky barrier diodes fabricated from (100)CoGa/Ga1-xAlxAs and CoAs/Ga1-xAlxAs showed good characteristics with low ideality factors, n<1.15. Good Schottky barrier behavior was also found for (100)ErAs/GaAs structures.

The morphology of a Ni(5nm), Au(45nm), Ge(20nm) ohmic contact with a ZrB2 (50nm) diffusion barrier, annealed to temperatures between 355°C and 485°C, was studied by TEM. The barrier was found to remain intact and unreacted after annealing. The contact annealed to 355°C reacted in the solid state to form αAu-Ga, Ge and orthorhombic NiGe phases. The morphology of contacts annealed above the melting point (∼ 380°C) consisted of two regions; type A contained αAu-Ca and NiGeAs, and type B contained αAu-Ga α′Au-Ga, NiGe and epitaxial Ge. αAu-Ga segregated to the contact pad edges at and above 403°C. The transition from rectifying to ohmic properties corresponded to annealing above the melting point of the contact. It was found that variations in contact resistance with temperature could be explained either by changes in the bulk or in the edge morphology.

The first epitaxial platinum gallium two (PtGa2) films have been grown on gallium arsenide (GaAs) (100) by co-evaporation of the elements under ultra-high vacuum conditions. An electron beam evaporator and a Knudsen cell were used to produce the platinum and gallium beams, respectively. The resulting films and bulk PtGa2 have been characterized by x-ray diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. The data confirm the PtGa2 stoichiometry and crystal structure of the films, and demonstrate their chemical stability on GaAs (100). This study supports the contention that PtGa2 can be a suitable, temperature stable contact material on GaAs substrates.

Crystallization temperature (Tc) of amorphous WSix films on GaAs was studied as a function of the Si/W ratio. The highest Tc of 875°C for a 20 min anneal was obtained for co-sputtered WSMi films with the Si/W ratio of 0.45 (31 at.% Si). The WSi0.45 films remained amorphous following implant activation anneal and served as a barrier to Ga and As outdiffusion. Pitting of GaAs under the contact was also prevented. The WSi0.45 composition corresponds to the eutectic point between the W and W5Si3 phases, which was explained by the strong glass-forming tendency of eutectic alloys. Amorpous WSi0.45 films formed stable Schottky contacts to n-GaAs and produced minimum reduction of carrier concentration in the substrate. Therefore, the Si/W ratio of 0.45 is suggested as optimal for the WSix refractory gate metallization in self-aligned GaAs MESFErs.

Reactions between Au and GaAs occurs during alloying of Au-based ohmic contacts on GaAs. The reaction and electrical properties of annealed Au/GaAs contacts have both been studied. The extent of the Au-GaAs reactions increased with annealing temperature, incorporated Ga and As into the Au film and left pits on the GaAs surface. The activation energy for these reactions was determined to be 17.6 kcal/mole. Analysis of size evolution of reaction pits on GaAs proved that GaAs regrows at long time annealing. A mixed GaAs dissolution-regrowth mechanism is proposed for annealing temperature and time similar to those used to form alloyed ohmic contacts. Increased surface carrier concentrations resulting from accumulation of dopants near the Au/GaAs interface is proposed to enhance ohmic contact formation.

We have demonstrated growth of high quality single crystal CoGa films on Ga1−xAlxAs. These films were fabricated in-situ by codeposition of Co and Ga on MBE grown Ga1−xAlxAs(100) surfaces. The elemental composition of the films was determined using Rutherford Backscattering (RBS) and in-situ Auger analysis. The structural quality of the films' surfaces was studied using RHEED (during deposition) and LEED (post deposition). RBS channeling was used to determine the bulk crystalline quality of these films.

For ∼500 Å CoGa films grown at ∼450°C substrate temperature, channeling data showed good quality epitaxial single crystals [χmin ∼7%] with minimal dechanneling at the interface.

Multilayered WSix films for use as gates in a self-aligned refractory gate process of GaAs MESFETs have been RF sputtered onto GaAs wafers under UHV background conditions in order to study their structure and morphology as well as their contact electrical properties. Annealed films deposited at 300°C with single layer thickness of 6 and 3 nm for W and Si respectively have a smooth morphology free from cracks and blisters and show a good adhesion to the substrate. Schottky diodes prepared on n-GaAs exhibit an almost excellent I-V characteristics with a barrier height of 0.73 V and an ideality factor of 1.11. In addition E - and D-FETs fabricated on implanted s.i. wafers have good electrical parameters with transconductances of 200 mS/mm at 1 μm gate length.

The mobility profile of electrons in active layer of GaAs MESFET has an inportant effect on the device performance. The mobilities at layers of different depth can be measured by changing the negative gate bias, but the electron mobility near the surface can't be measured yet due to the depletion of electrons in the surface layer. This paper introduces a differential d.c. equivalent model, in which the Schottky barrier can be forward biased and the gate current correction is properly included. Applying this model, we can precisely calculate the drift and gecmetrical magnetic resistance mobilities very close to the surface layer.

MIS diodes were fabricated using Pd, Ni and Au- contacts on n-InP covered by a 40 Å chemically-grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3 + some InPO3 near the surface and mixed oxide + InP near the interface. Pd-devices gave the highest barrigr height of 0.80 eV and lowest reverse saturation current density of 3×10−8A/cm2. I-V-T and C-V-T data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism. Richardson plots gave good straight lines when empirically corrected using øB/n instead of just øB.

The status and progress of AlGaAs/GaAs heterojunction bipolar transistor integrated circuits are reviewed. The challenge of fabricating large-scale integrated circuits using heterojunction bipolar transistors is discussed. Specifically, the issues related to low defect epitaxial materials, localized impurity doping techniques, simple and reliable ohmic contacts, and multilevel interconnects are examined.

A doped channel heterojunction Field Effect Transistor (Metal-Doped Channel Field Effect Transistor, MEDFET) was fabricated using a molecular beam epitaxially (MBE) grown structure and excimer laser processed TiW-silicide ohmic contacts and TIW-Si gate metallization. The device was characterized at X-band frequencies in order to investigate the potential benefits of the semiconductor MBE structure and the potential stability of the laser processed TiW/Si electrode metallizations.

Low temperature photoluminescence was studied in a large number of pseudomorphic HEMT's having an InxGa1−xAs quantum well. The spectra show strong qualitative differences when the Fermi level is above or below the second conduction subband, and in the latter case they are power dependent. A slight enhancement is seen at the Fermi edge only when it lies close to the higher subband. Excellent agreement is found between the measured Fermi energy and the two-dimensional carrier density in the well.

Scaling of the In0.52Al0.48As insulator thickness of In0.52Al0.48As/n+-In0.53Ga0.47As MIStype FET's is experimentally found to result in a drastic drop of performance below 200 Å. This is demonstrated to arise from an increase in the sheet resistance of the extrinsic portions of the device that accompanies insulator scaling. In order to solve this problem, a recessed-gate dopedchannel MISFET with a very thin (300 Å) n+-In0.53Ga0.47As cap layer has been fabricated. A 1.5 μm long gate device showed a transconductance of 285 mS/mm and a current-gain cut-off frequency of 19.4 GHz. This result proves the ability of a thin n+-In0.53Ga0.47As cap to reduce source resistance and improve device performance. The fabricated recessed-gate structure is a promising candidate for high-performance scaled MIS-type FET's based on thin, heavily-doped In0.53Gav0.47 As channels.

The narrow and direct bandgap of indium antimonide is frequently used to good advantage in detection of light in the infra-red region; however, to date little use has been made of the high mobilities associated with this material. Although its high intrinsic carrier concentration generally necessitates operation at cooled temperatures, higher speeds and the advantage of integrating other devices on-chip with the infrared detectors encourages the development of an active device technology on this semiconductor. Considering its small bandgap, the problems associated with good p-n junctions may favor the MISFET in this application. Surprisingly, little has been done toward this goal, though structures such as chargecoupled- devices [1], focal array detectors [2], and a few insulated gate FETs [3,4] have been fabricated. In this paper we present the results of our recent work toward the development of a fabrication technology for InSb MISFETs. Specifically, we have conducted a study of etchants, metal contacts, and dielectrics for application to mesa-structure, insulated gate field transistors.

GaAs/AlGaAs N-p-n heterojunction bipolar transistor (GaAs HBT) device and integrated circuit technology which offers key advantages over advanced silicon bipolar and III-V compound field-effect transistors is maturing towards system insertion. The TRW device and IC fabrication process, basic HBT dc and RF performance, examples of device and IC applications, and technology qualification work are presented and serves as a basis for discussing overall technology issues and impact. A relaxed 3-μm emitter-up, self-aligned base ohmic metal (SABM) HBT process and simplified molecularbeam epitaxial profiles are used for near-term producibility. The HBTs have simultaneous fT, fmax≈20–40 GHz and dc current gain ß≈50–100 at collector current density JC=3 kA/cm2 and Early voltage VA≈200–300 with capability for MSI-LSI integration levels. Versatile dc-20 GHz analog, 3–6 Gb/s digital, and 2–3 Gs/s A/D conversion functions are demonstrated with a common 3-μm SABM HBT process which facilitates single-chip multifunctional capability. Key improvements are realized over Si bipolar and GaAs-related FET (e.g. MESFET and HEMT) approaches in operational frequency, gain-bandwidth product, harmonic distortion, 1/f noise, power consumption, and size reduction.