G. Y. Robinson

Metallurgical and electrical properties of alloyed Ni/AuGe films on n-type GaAs

Abstract An experimental study of the alloying characteristics of a composite thin-film structure which is often used as an ohmic contact to GaAs is presented. A AuGe layer of eutectic composition covered by a thin-film of Ni and deposited on n-type epitaxial GaAs is investigated in order to better understand the relationship between the alloying behavior and the electrical properties of the contact. The barrier energy ϕBn and the specific contact resistance of the Ni/AuGe/GaAs system is measured for a wide range of alloy temperatures and times. The metallurgical properties of the Ni/AuGe/GaAs system are obtained with Auger electron spectroscopy and scanning electron microscopy. Auger spectroscopy combined with in situ sputter etching is used to determine depth-composition profiles for all constituents of both as-deposited and alloyed Ni/AuGe/GaAs contacts. In samples heat-treated below the AuGe eutectic temperature, Ni is found to move rapidly through the intervening AuGe layer to collect at the GaAs interface, and the effective value of ϕBn rises to the value characteristic of Ni/GaAs Schottky diodes. For heat-treatment above the AuGe eutectic temperature, ohmic contact behavior is observed, and uniform alloyed contact surfaces are found to result from the presence of Ni at the GaAs interface. Ga outdiffusion and surface accumulation resulting from GaAs dissociation occurs for all alloy temperatures and times. The Ga outdiffusion appears to be characterized by a very low activation energy.

Band offset of GaAs/In0.48Ga0.52P measured under hydrostatic pressure

Low‐temperature photoluminescence spectra of an In0.48Ga0.52P alloy and a p‐type GaAs/In0.48Ga0.52P multiple quantum well, both grown by molecular beam epitaxy, have been obtained under hydrostatic pressures from 0 to 6 GPa. The zero‐pressure extrapolation of the InGaP(X) to GaAs(Γ) transitions yields a 0.40±0.02 valence‐band offset, and hence only a small, 0.06 ± 0.02 eV, conduction‐band offset. These offset values are in agreement with measured values of the confinement energy versus well width.

Optical properties of GaAs on (100) Si using molecular beam epitaxy

Undoped GaAs layers have been grown on (100) oriented Si by molecular beam epitaxy and have been studied using photoluminescence, photographic, and x‐ray measurements. To minimize antiphase disorder, an As primer layer was successfully used to initiate the polar on nonpolar growth. Photoluminescence spectra show the presence of five bands into which the luminescence from each sample falls. The energy variation within any given band was less than 4 meV. X‐ray and photoluminescence analysis appear to indicate some strain in the crystal. Although very preliminary, the results obtained indicate that GaAs on Si can potentially be used for a number of hybrid ciruits.

High quality quantum wells of InGaP/GaAs grown by molecular beam epitaxy

High quality quantum wells of GaAs confined by barriers of InGaP have been grown by gas‐source molecular beam epitaxy. High‐resolution lattice images obtained with transmission electron microscopy of single quantum wells reveal high quality interfaces for both the normal InGaP/GaAs and the inverted GaAs/InGaP interface. Multiple‐line low‐temperature photoluminescence emission is observed for the thinnest GaAs quantum well. The range of well thicknesses examined was 0.6–5.2 nm, with the smallest well producing a quantum confinement energy shift of over 410 meV, corresponding to photoluminescence emission at 640 nm (1.94 eV) from GaAs.

Internal photoemission and energy‐band offsets in GaAs‐GaInP p‐I‐N heterojunction photodiodes

Internal photoemission has been observed in GaAs‐Ga0.52In0.48P p‐I‐N heterojunction photodiodes grown by gas source molecular beam epitaxy. Threshold energies associated with this photocurrent mechanism have been accurately measured. Simple analysis provides a precise determination of the energy‐band discontinuities in this heterostructure material system. The results indicate a conduction‐band discontinuity of ΔEc=108±6 meV at room temperature.Internal photoemission has been observed in GaAs‐Ga0.52In0.48P p‐I‐N heterojunction photodiodes grown by gas source molecular beam epitaxy. Threshold energies associated with this photocurrent mechanism have been accurately measured. Simple analysis provides a precise determination of the energy‐band discontinuities in this heterostructure material system. The results indicate a conduction‐band discontinuity of ΔEc=108±6 meV at room temperature.

Schottky contacts on chemically etched p‐ and n‐type indium phosphide

The Schottky‐barrier energy φB for Al, Ni, Co, Pd, Au, and Ag contacts on chemically etched 〈100〉 surfaces of both p‐ and n‐type InP were measured and the metallurgical behavior of the contact structures were studied using Auger electron spectroscopy. φB was found to be a function of the chemical reactivity of the contact metal with the InP substrate. Extensive outdiffusion of In was observed in the Au and Ag contacts. The results indicate that the chemical effects at the metal‐semiconductor interface are a determining factor in the formation of InP Schottky barriers.

Pd/Ge contacts to n-type GaAs

Abstract Sintered metal-semiconductor contacts, formed by thin, evaporated layers of Pd and Ge on n -type GaAs, were studied using Auger electron spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, current-voltage measurements, and capacitance-voltage measurements. Prior to sintering, the as-deposited Pd/Ge/GaAs contacts were rectifying and exhibited a reproducible Schottky barrier energy φ Bn of 0.67±0.02 eV. Auger analysis indicated the initial behavior of the contact structure, upon sintering, to be an interdiffusion and reaction of Pd and Ge on a non-reacting GaAs substrate. Two germanide phases, Pd 2 Ge and PdGe, were identified using X-ray diffraction and Auger analysis. The intervening Ge layer prevented the reaction of Pd with the GaAs substrate at low temperatures. Because of the PdGe reaction, φ Bn increased to approximately 0.85 eV. Sintering at higher temperatures (i.e. between 300 and 400°C) produced additional reactions between Pd and the GaAs substrate. The electrical properties of the contact remained rectifying and φ Bn exhibited little change from the value of 0.85 eV with the interdiffusion of Pd, Ga, and As. Sintering above 400°C resulted in the formation of ohmic contacts. The diffusion of Ge to the GaAs interface was found to correlate with the onset of ohmic behavior. Current conduction in the contact was best described by thermionic-field emission theory, and a specific contact resistance of 3.5 × 10 −4 Ω-cm 2 was obtained after sintering above 550°C, independent of the initial impurity concentration in the substrate. Over the entire range of sintering temperatures (i.e. at or below 600°C), the interaction between the thin-film layers appeared to be governed by diffusion-controlled, solid-phase processes with no evidence of the formation of a liquid phase. As a result, the surface of the contact structure remained smooth and uniform during sintering.

Ultrafast graded double‐heterostructure GaInAs/InP photodiode

Ultrafast graded double‐heterostructure GaInAs/InP p‐i‐n photodiodes grown by gas source molecular beam epitaxy have been fabricated on an InP semi‐insulating substrate. The graded band‐gap layers and the double heterostructure reduce carrier trapping effects and diffusion current and the resulting response of a 5 μm×5 μm device was measured by electro‐optic sampling to be 5 ps full width at half maximum (FWHM). The deconvolved impulse response is 3.8 ps FWHM.

A comparison of Pd Schottky contacts on InP, GaAs and Si

Abstract The Schottky-barrier energy φB of Pd contacts on InP, GaAs and Si were measured and the metallurgical behavior of the contact structures were studied using Auger electron spectroscopy. A carefully processed set of samples were used to show conclusively that φB is greater on p-InP that on n-InP, unlike the behavior of GaAs and Si Schottky diodes fabricated at the same time with similar processing steps.

A study of Schottky contacts on indium phosphide

The Schottky‐barrier energy φB for Al, Ni, Pd, Co, Au, and Ag contacts on chemically etched 〈100〉 surfaces of both p‐ and n‐type InP was measured and the metallurgical behavior of the contact structures was studied using Auger‐electron spectroscopy. No simple linear relationship could be found between the measured Schottky barrier energies on InP and the work functions or the electronegativities of the contact metals. Therefore, the results could not be explained in terms of the traditional Schottky and Bardeen theories. However, a very well defined relationship was observed between the Schottky barrier energies and the heats of reaction per formula unit ΔHr for the most stable metal phosphides that could be formed between the contact metals and the InP substrate. The contact metals Au and Ag whose phosphides are less stable than InP (i.e., ΔHr >0) produced diffuse interfaces, characterized by extensive outdiffusion of In, and yielded low values of φBp, the Schottky‐barrier energy on p‐type InP; whereas t...