B. Tuck

Role of Point-Defects in the Silicon Diffusion in Gaas and Al0.3ga0.7as and in the Related Superlattice Disordering

The mechanism of silicon diffusion in GaAs, Al0.3Ga0.7As, and the silicon diffusion‐induced layer disordering of multiquantum wells have been studied by photoluminescence, secondary‐ion‐mass spectroscopy, and transmission electron microscopy across a corner of a wedge‐shaped sample. The diffusion source was a grown in highly Si‐doped layer. The main photoluminescence properties of point defects in GaAs and Al0.3Ga0.7As are reviewed to interpret the experimental data. The depth profile of the photoluminescence allows the spatial correlation between the luminescence spectra and the Si concentration profile obtained from secondary‐ion‐mass‐spectroscopy measurements. On the basis of the photoluminescence results, the physical processes occurring during the Si diffusion are discussed. Frenkel defects (pairs of element‐III vacancies and interstitials) are generated in the highly Si‐doped region. The element‐III interstitials rapidly diffuse towards the surface where they react with the element‐III vacancies gen...

Investigation of Au Schottky contacts on GaN grown by molecular beam epitaxy

Gold Schottky diodes have been fabricated, for the first time, on n-type GaN grown by molecular beam epitaxy. These diodes have been studied by I - V, C - V and deep-level transient spectroscopy. The conduction process inside the diodes is shown to be by thermionic field emission. The barrier height of 1.1 eV compares well with Au Schottky diodes manufactured from n-GaN grown by metalorganic chemical vapour deposition. However, there is evidence to suggest that the grown-in deep levels are different for the two growth techniques.

Transition metal diffusion in InP: Photoluminescence investigation

The 3d transition metals (TM’s) from Cr to Cu introduced into InP by diffusion are studied using low temperature photoluminescence (PL). Luminescence bands from Mn, Co, and Cu are observed whereas for the remaining TM’s, Cr, Fe, and Ni, no optical effects related to the diffused species are detected. This behavior is found to correlate with electrically active, compensating deep acceptor levels found for Mn, Co, and Cu in C‐V measurements, but not for the other TM’s. For Mn diffusions at 800u2009°C deep level PL peaking at 1.15 eV ascribed to substitutional Mn2+In is observed. For the case of Cu three different PL bands are found peaking at 1.2, 1.17, and 0.99 eV, respectively. It is speculated that the 1.0‐eV band may arise from CuIn centers. The higher energy bands arise from Cu‐related complexes. Reasons for the electrical and PL activity of Mn and Co, but not for the adjacent fast diffusing TM’s Cr and Fe which are electrically active in growth doped material, are discussed in terms of the particularly de...

Electrical properties of n-GaN/n+-GaAs interfaces

Abstract Current–voltage and capacitance-voltage characteristics of an n-GaN/n+-GaAs substrate heterojunction have been measured over the temperature range from 120 to 360xa0K. It was found that, depending on the GaAs substrate temperature, the heterojunction behaves either as a back-to-back diodes structure or as a metal–insulator–semiconductor (MIS) structure. From the reverse bias saturation currents, an activation energy was estimated and was found to be 0.25 and 0.16xa0eV for the samples which behaved as MIS structures.

Investigation of aluminium ohmic contacts to n-type GaN grown by molecular beam epitaxy

Using epi-layers of different doping concentrations, we have investigated aluminium contacts on n-type gallium nitride grown by plasma source molecular beam epitaxy. To achieve repeatable and reliable results it was found that the semiconductor needed to be etched in aqua-regia before the deposition of the contact metallization. Scanning electron micrographs of the semiconductor surface show a deterioration of the semiconductor surface on etching. The specific contact resistivity of the etched samples were, however, superior. Annealing the contacts at produced contacts with the lowest specific contact resistance of . The long-term aging of these contacts was also investigated. The contacts and the sheet resistance were both found to deteriorate over a three-month period.

Diffusion-induced defects in GaAs by zinc and the effects of post-diffusion anneal

The crystallographic defects generated during the diffusion of zinc into GaAs have been studied using transmission electron microscopy and chemical etching techniques. By observing the effects of arsenic pressure on the defect density and the zinc penetration, the annihilation of the diffusion‐induced defects in relation to the surface stoichiometry was investigated. It was found that the dissolution of the defects within the crystal is mainly caused by the out‐diffusion of the diffusion‐induced Ga interstitials to the surface. This is also supported by results obtained from post‐diffusion annealing of the samples under different arsenic pressures. In addition, the possible inclusion of arsenic atoms in the interstitial dislocation loops found in GaAs is also discussed.

Arsenic pressure dependence of group III atom interdiffusion in GaAs-AIAs single-well heterostructures

Annealing experiments were performed on undoped GaAs-AIAs single well heterostructures grown by MBE. The annealing experiments were performed in evacuated and sealed silica ampoules. The temperature and time of annealing were fixed at 1000 ‡C and 4 h respectively while the As vapour pressure in the ampoules was varied from dissociative pressure to approximately 1.08 × 105Pa. Compositional profiles were obtained using dynamic SIMS. It was found that the amount of intermixing in the layers was dependent both on As pressure and distance from the sample surface. In contrast with previous results, the complex variation of interdiffusion with As pressure observed in this work cannot be interpreted in terms of interdiffusion via group III vacancies and interstitials only.

The effect of arsenic pressure on the diffusion-induced disordering of tin in AlAs-GaAs superlattices

Tin diffusions into AlAs-GaAs superlattices have been performed in sealed silica ampoules. The present experiments, for the first time, examine the effect of As on tin induced disordering. SIMS and shallow-angle bevel revealed that both the tin surface concentration and the width of the disordered region are increased when a higher arsenic pressure inside the ampoule is used. Such dependence on the arsenic pressure is explained by the diffusion via a negatively charged complex which may take the form of [VGaSnAsVGa]−. The disordering effect could be attributed to the diffusion of Ga vacancies associated with the migration of the complexes. However, a more likely explanation is the Fermi-Level effect which has been proposed to explain the enhancement of the interdiffusion in Si doped samples.

Exact solutions for substitutional-interstitial diffusion in semiconductors

A discrete model for substitutional-interstitial diffusion in III-V semiconducting materials, previously used to obtain a fitting of computed results to experimental data, is reviewed and its continuum form as a partial differential equation is obtained. The solution is presented and the physical interpretation of this solution using the physical model and the experimental results is discussed.

Annealing-induced dislocation loops in Si-doped GaAs-AIAs superlattices

Dislocation loops were observed to form in the Si-doped layer of an MBE-grown GaAs-AIAs superlattice structure as a result of annealing. The density and size of the loops, as estimated by cross-sectional TEM, were shown to depend on the As pressure, annealing time and temperature. The loops are proposed to nucleate as a result of the undersaturation of As vacancies, caused by the site-switching of Si atoms from group III sites to As sites. The deficient As vacancies are restored by the crystal which generates Frenkel pairs. Consequently, As interstitials are created in excess. These latter species precipitate in the form of platelets of interstitials which produce dislocation loops. As the annealing time increases and more excess interstitials are accommodated, the loops gradually dissociate by recombination of the interstitials forming the loops with vacancy pairs.