InP mixer diodes processed with Ag/TiW/Au Schottky diodes have exhibited a noise figure of 6.5-7.0 dB at 94 GHz. InP surface preparation is shown to be critical in diode performance. An indium-stabilised surface has resulted in a barrier height of 0.45 eV.

The recrystallization and epitaxial regrowth of amorphous silicon layers on molecular beam epitaxial (MBE) silicon at 650 °C is described. MBE silicon layers were deposited at 650 °C followed by deposition of amorphous layers at 100–400 °C. Subsequent solid phase epitaxial regrowth of these layers has been achieved at 650 °C.

Thin films amorphous WSi and TiWSi diffusion barriers have been studied on GaAs and InP surfaces for the purpose of establishing their reliability for ohmic contacts and Schottky barriers, particularly under high temperature stress. The amorphous films were formed by a new method in which alternate layers of tungsten or TiW and silicon were sputter deposited to a total thickness of about 1300 Å and subsequently annealed near the glass transition temperature Tg(≈500°C). Electron channeling and reflection electron diffraction were used to determine the amorphous nature of the films as deposited and after 4 h anneals near Tg. The as-deposited films had interfacial amorphous regions with compositions determined by interfacial reactions during the sputtering process. As-deposited WSi films showed a weak channeling pattern which came from the unreacted polycrystalline tungsten layers. From Auger electron spectroscopy (AES) sputter profiles, it was concluded that the amorphous regions were at the WSi interfaces which had the required tungsten-to-silicon composition ratio. After annealing at 500 °C for 4 h, the films were completely amorphous with no marked evidence of crystallization, indicating interfacial reactions extended completely into the tungsten layers. High magnification scanning electron microscopy (by a factor of 20 000) examination of the films after annealing revealed smooth and continuous surfaces with no evidence of grain boundaries. Diffusion along grain boundaries between gold and GaAs or InP in these amorphous thin films was thus almost completely eliminated. Interdiffusion of gold in layered structures (e.g. Au/(WSi)/GaAs) was studied by AES sputter profiling techniques. No interdiffusion of gold or GaAs was observed after 16 h anneals at 400 °C. With Au/(WSi)/InP structures, no interdiffusion was observed after 8 h anneals at 450 °C. These results are significant improvements over those for previous polycrystalline diffusion barriers (e.g. TiPt) which degrade after 1 h at 350 °C. Based on the AES sputter profiles, the diffusion coefficients in WSi amorphous thin films were found to be less than 3 × 10−18 cm2 s−1 at 400 °C for gold, gallium and arsenic and less than 6 × 10−18 cm2s−1 at 450 °C for gold, indium and phosphorus.

Amorphous W-Si, TiW-Si and Ni-Si diffusion barriers have been developed for GaAs field effect transistors to achieve improved reliability of ohmic contacts and Schottky barriers, particularly in high temperature ambients. The amorphous films were formed by a new method in which alternate layers of 500A° (W, TiW or Ni) and 300A° Si were sputter deposited and subsequently annealed just below the glass transition temperature Tg (~ 500°C) and rapidly cooled. Electron channeling was used to determine the amorphous nature of the film after 4 hr. anneals at Tg. Amorphous regions were present in the deposited films due to the rapid quenching process of sputter deposition. After annealing at 500°C for 4 hours, the films were completely amorphous with no evidence of crystallization. High magnification SEM (20,000X) examination of the films after annealing revealed smooth and continuous surfaces with no evidence of grain boundaries. Diffusion along grain boundaries between Au and GaAs in Au/W-Si/GaAs structures is thus virtually eliminated, thereby minimizing both electromigration and contact reactions. Interdiffusion in Au/W-Si/GaAs and Au/TiW-Si/GaAs layers was studied by Auger electron spectroscopy sputter profiling techniques. No interdiffusion of Au or GaAs was observed after 8 hour anneals at 450°C. This is a significant improvement over previous polycrystalline diffusion barriers (e.g., TiPt) which interdiffuse after 2-3 hours at 350°C. Two micron gate (small signal) FETs were fabricated with amorphous TiW-Si gates and AuGeNi ohmic contacts. Accelerated life tests were carried out at 300°C.

Thin substrateless MBE GaAs diodes have been processed for mixer applications. MBE growth of an inverted n/n+ GaAs structure on Ge was achieved. The Ge substrate was removed by preferential etching. A noise figure of less than 6.0 dB at 94 GHz was obtained.

This special issue on GaAs Integrated Circuits covers a selection of the best papers presented at the 1981 IEEE GaAs Integrated Circuits Symposium held in San Diego, CA.

Epitaxial Ge/GaAs low-barrier-height Ti-Mo-Au Schottkybarrier diodes exhibit a noise figure of 6.5 dB at 36 GHz and at 0.75 mW of local oscillator (l.o.) power. These diodes represent significant improvement over standard GaAs-Ti diodes at low power levels.

Ge films deposited by vacuum deposition at 425‡C are generally p-type. This paper discusses the use of pulsed-electron beam annealing and ion implantation to modify the carrier concentration of such films. Electron beam annealing has been used to reduce the carrier concentration by more than a factor of 30 and n-type films have been obtained by phosphorus implantation and subsequent thermal annealing. TEM, RBS and Hall measurements have been used to characterize the films. The electrical properties of the as-grown films are believed to be defect dominated.

In this letter it is shown that both p- and n-type Ge vacuum-deposited films can be obtained on the same GaAs substrate during the same pump-down. p-type films are generally obtained if films are deposited immediately on the substrate at temperature ⩾300 °C, cooled down from outgas temperature 575 °C. n-type films are obtained consistently if the same substrate is then held below 300 °C for about 100 min before deposition. The low electron mobility observed for n-type Ge films leads to the conclusion that the properties of the films are determined by As compensation of p-type defects inherent in the films.

A Ge heterojunction-gate GaAs f.e.t. has been developed using p-type epitaxial Ge gates deposited by vacuum evaporation on heated n-type GaAs substrates. Boron-ion implantation of the gate and an aluminium overlay was used to lower the gate resistance. A typical 8 µm gate-length device exhibited a noise figure of 5.2 dB with 4.5 dB associated gain at 1.8 GHz.

Using a thin Ge-GaAs structure, barrier height lowering of 0.2-0.3 eV has been attained. These X-band diodes have a noise figure of 6.0-6.5 dB at 0.75-1.0 mW of local-oscillator power. The diodes have superior power-handling capability with Pt-Ti-Mo-Au metallisation.

Epitaxial growth of (100) GaAlAs and Al was achieved on (100) n-GaAs substrates using vacuum deposition in an ultrahigh vacuum system. In situ Auger electron analysis, microspot Auger electrospectroscopy, LEED, and reflection electron diffraction was used to characterize the films. Regions of GaAlAs and Al were identified. Electrical measurements indicated the presence of a stable Schottky barrier with a barrier height of 0.76 eV.

Si layers deposited on Au-Si substrates at temperatures above 380 °C are epitaxial with the underlying Si substrate. The layers analyzed contain a high density of microtwins which is the main factor resulting in dechanneling in the aligned RBS spectrum. The deposited layers also contain stacking faults and residual Au inclusions adjacent to primary twins.

Ohmic contacts to n-type GaAs have been developed using epitaxial Ge films on GaAs alloyed with Ni overlayers by solid state diffusion at temperatures of 450°C - 550°C. These contacts have applications to high reliability, high temperature microwave devices. The Ge films were deposited epitaxially on heated GaAs substrates. Reflection electron diffraction of the Ge layers prior to deposition of the Ni overlayers reveals the presence of high quality single-crystalline films. Interdiffusion at the Ge-GaAs and Ni/Ge-GaAs interfaces was examined by Auger Electron Spectroscopy (AES) sputter profiling techniques A very sharp profile is observed at the as deposited Ge-GaAs interface. Even after sintering, there is very little penetration of Ge into GaAs in the absence of Ni. With the presence of a Ni overlayer, significant interdiffusion between Ge and GaAs is revealed by AES profiles, thus indicating the presence of an n + layer at the Ni/Ge-GaAs interface. The presence of a Ge doped n + layer was examined by electrical measurements using n- and p-GaAs substrates.

Silicon films deposited on Au/Si layers at deposition temperatures at or above 380 °C are single crystal, while Si films deposited on Si with a native oxide are amorphous up to 500 °C and ordered polycrystalline above 500 °C. The initial gold (300 Å) deposit migrates to the growing epitaxy surface where it nucleates in clusters. RBS and AES analysis indicated that 0.1 at.% gold remains distributed throughout the epitaxial film.

Thin epitaxial films of silicon have been grown at 600 °C on (111) silicon surfaces by vacuum deposition. The silicon deposition and growth was performed subsequent to a hot deposition (125 °C) of 300-Å gold film on the substrate.

Amorphous germanium films were implanted to high boron levels, ∼1021/cm3 peak concentrations. Before and after implantation the conductivity measurements fit the relation logσ∼T−1/4 and no evidence of intravalence absorption was observed indicating that the Fermi level was near the center of the band gap. Thermoelectric power measurements indicated that the samples were weakly n type before implantation and p type after implantation. The position of the fundamental absorption edge shifted to lower energy upon implantation and to higher energies upon subsequent anneals. Implanted recrystallized films were strongly p type, exhibited intravalence absorption, and had very low dc activation energies.