A. Turos

Gold-based ohmic contacts on III–V compounds: Thermally induced reactions between metallization and the semiconductor compound☆

Au/Zn/Au and AuBe layers were used to prepare ohmic contacts on p-type GaAs, GaP and InP. Rutherford backscattering spectrometry with 2 MeV He+ ions, secondary ion mass spectrometry, X-ray diffraction analysis and scanning electron microscopy were used to study the thermally induced reactions accompanying the formation of ohmic contacts. A change in the ohmic behaviour in the sequence GaAs, InP, GaP occurred upon heating. A marked ability of the group III element in the semiconductor substrate to react with gold appeared to be a common feature of the systems investigated. No reaction product involving the group V element was observed in contacts on GaAs and GaP, whereas the Au2P3 phase was identified in contacts on InP. The zinc dopant was found to form the intermetallic phases AuZn and Au3Zn with gold, and an increase in the content of the beryllium dopant resulted in the retardation of the metal-semiconductor reaction.

Ion beam characterization and engineering of strain in semiconductor multi-layers

Abstract The objective of this work is to measure and engineer the strain in III–V compound semiconductor multi-layers using ion beams, which leads to spatial band-gap tuning for the integration of optoelectronics devices. Strained layer superlattices have been of unique interest due to their ability to tune the band gap, which depends on the strain at the interface. Therefore the strain measurements at the interface are of great interest. A large area two-dimensional positions sensitive Δ E − E detector telescope and a fully automated high energy channeling facility have been developed at NSC, New Delhi. An overview of the series of ERDA, RBS, Channeling, HRXRD and ion beam mixing experiments performed in this direction will be discussed in this paper.

Ion beam studies in strained layer superlattices

Abstract The potential device application of semiconductor heterostructures and strained layer superlattices has been highlighted. Metal organic chemical vapour deposition grown In 0.53 Ga 0.47 As/InP lattice-matched structure has been irradiated by 130 MeV Ag 13+ and studied by RBS/Channelling using 3.5 MeV He 2+ ions. Ion irradiation seems to have induced a finite tensile strain in the InGaAs layer, indicating thereby that ion beam mixing occurs at this energy. Other complementary techniques like high resolution XRD and STM are needed to conclude the structural modifications in the sample.

Investigation of Strain in AlGaN/GaN Multi Quantum Wells by Complementary Techniques

Al0.49Ga0.51N (12 nm)/GaN (13 nm) Multi Quantum Wells of 15 periods are grown on sapphire by MOCVD technique. GaN/AlN, each of thickness 200 nm and 20 nm respectively, are used as buffer layers between substrate and epilayer to incorporate the strain in epilayers. It is a well established technique to engineer the band gap in AlxGa1−xN by adjusting alloy composition. These samples are used in visible & UV light emitters. In the present study, we employ a photoluminescence technique to estimate the composition and luminescence peak positions of AlGaN and GaN. Crystallinity and quality of interfaces have been studied by Rocking curve scan. The Threading Dislocations formed at the GaN buffer layer travel across the entire layers to the surface to form good quality films. Photo‐luminescence results show a very sharp GaN peak at 3.4 eV, as observed and reported by others, which shows that samples are free from point defects.

The Influence of Growth Temperature on Oxygen Concentration in GaN Buffer Layer

The influence of growth temperature on oxygen incorporation into GaN epitaxial layers was studied. GaN layers deposited at low temperatures were characterized by much higher oxygen concentration than those deposited at high temperature typically used for epitaxial growth. GaN buffer layers (HT GaN) about 1 μm thick were deposited on GaN nucleation layers (NL) with various thicknesses. The influence of NL thickness on crystalline quality and oxygen concentration of HT GaN layers were studied using RBS and SIMS. With increasing thickness of NL the crystalline quality of GaN buffer layers deteriorates and the oxygen concentration increases. It was observed that oxygen atoms incorporated at low temperature in NL diffuse into GaN buffer layer during high temperature growth as a consequence GaN NL is the source for unintentional oxygen doping.

Anti-diffusion barriers for gold-based metallization to GaN

We propose a new metallization scheme to p-GaN, where thin-film transition metal nitrides have been applied to improve thermal stability of gold-based metallization. In this metallization scheme the Pd/Au bilayer was used to form low-resistivity ohmic contact to p-GaN, while Ta-Si-N, Ti-Si-N, and Ti-W-N anti-diffusion barriers were used to protect contact metallization from interaction with Au overlayer. We present the details of optimization of process parameters of barrier layer fabrication and show that Ta 0.34 Si 0.25 Ni 0.41 and Ti 0.26 Si 0.0.17 Ni 0.57 thin films fabricated by reactive magnetron sputtering show excellent barrier properties under high temperature stress.

Oxygen out-diffusion and compositional changes in zinc oxide during ytterbium ions bombardment

Oxygen release and out-diffusion in zinc oxide crystals during heavy ions bombardment has been suggested by many experimental techniques. In this work we have employed secondary ion mass spectrometry to study ZnO implanted with ytterbium ions. Our measurements confirm formation of an oxygen-depleted layer and oxygen out-diffusion and agglomeration at the surface. Moreover, an average compositional change in a heavily damaged near-surface region can also be monitored. This reproducible measurement procedure with subnanometer depth resolution allows to localize precisely these altered layers at the depth of 14-28 nm (oxygen-depleted layer) and 9 nm (maximum of the amorphized region). Such precise measurements may prove to be valuable for further characterization of ion beam induced defects in wide bandgap compound semiconductors and optimization of optoelectronic devices based on these materials.

Structural Characterization of GaN Epitaxial Layers Grown on 4H-SiC Substrates with Different Off-Cut

The influence of surface preparation of 4H-SiC substrates on structural properties of GaN grown by low pressure metalorganic vapour phase epitaxy was studied. Substrate etching has an impact on the crystallographic structure of epilayers and improves its crystal quality. The GaN layers were characterized by RBS/channelling and HRXRD measurements. It was observed that on-axis 4H-SiC is most suitable for GaN epitaxy and that substrate etching improves the crystal quality of epilayer.

Ion Beam Studies of Strains/Defects in Semiconductor Multilayers

High Resolution X‐Ray Diffraction (HRXRD) studies have been performed to study the effects of Swift Heavy Ion (SHI) irradiation on In0.53Ga0.47As/InP lattice matched superlattice. Sample under the study have been irradiated using 130 MeV Ag ions to two different fluences (5 × 1012 ions/cm2 & 5 × 1013 ions/cm2). Pre and post irradiation annealing (RTA) studies have also been performed. A finite tensile lattice strain has been introduced due to the intermixing caused by ion irradiation and/or annealing processes. The superlattice period is found to increase due to ion irradiation and annealing processes. The superlattice structure used in this work was grown by Metal Organic Chemical Vapor‐phase epitaxial Deposition (MOCVD). Ion channeling measurements were earlier performed on the low dose sample. Channeling and HRXRD measurements show good crystalline/interface quality of pristine and processed samples. HRXRD also indicates the existence of the sharp boundaries across the superlattice interfaces. A decrea...

Reciprocal Space Mapping and Reflectivity Investigations of Epi‐Ready InP Substrate

InP single crystals are used to the growth of three-component epitaxial layers and superlattices. Triple crystal X-ray diffractometry and reflectometry have been used to determine defects in InP epi-ready wafers caused by the mechanical treatment. Reciprocal space maps around 400 lattice points were separately made for mechanically polished wafers before and after etching treatment. The lattice imperfections have been studied by measuring the diffusion scattering. The surface morphology has been controlled by means of X-ray reflectometry.