T. Srinivasan

Ion beam induced modification of lattice strains in In0.1Ga0.9As/GaAs system

Abstract The effects of 150 MeV Ag ion irradiation on the molecular beam epitaxially grown In0.1Ga0.9As/GaAs samples have been studied using high resolution X-ray diffraction (HRXRD). Our earlier experiments suggest that the compressive strain will decrease due to ion beam mixing effects in an initially strained system. Similarly a tensile strain will be induced in an initially lattice matched system. These studies are being performed to explore the possibility of spatial bandgap tuning for the integration of optoelectronics circuits. Here we present a systematic study to understand the effects of ion fluence and the initial strain/layer thickness on the modification of strain. Strain measurements are performed using HRXRD by determining the angular shift in the layer peak position with respect to that of the substrate peak. Substrate peak broadens with ion fluence due to the implantation effects at the end of the ion range (∼13 μm). However, the thin InGaAs layer and the substrate region near to this layer will not be affected. It is shown that the Swift Heavy Ion induced mixing can alter the lattice strain at room temperature without loss of the quality of the structure.

Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

We present surface photo-voltage (SPV) measurements on molecular beam epitaxy (MBE) grown single quantum well (SQW) laser structures. Each layer in the hetero-structure has been identified by measurement of the SPV signal after a controlled sequential chemical etching process. These results have been correlated with high resolution x-ray diffraction and photoluminescence (PL) measurements. Quantum confined Stark effect and the carrier screening of electric field have been taken into consideration both theoretically and experimentally to account for the differences observed in SPV and PL results. It is shown that SPV can be used as a very effective tool for evaluation of hetero-structures involving multiple layers.

Automation of Channeling Experiment for Lattice Strain Measurements Using High Energy Ion Beams

40 MeV Si channeling studies have been performed on the strained In0.1Ga0.9As layer grown on GaAs substrate using Molecular Beam Epitaxy (MBE). Three samples with different layer thickness have been investigated in this study. Channeling experiment has been fully automated so as to minimize the radiation damage. Suitable software and hardware have been developed to control the precision goniometer using the CAMAC (Computer automation and control) based data acquisition system. In low energy He channeling, strain measurements are often misled by the beam steering effects caused due to broad critical angles if the strain is very low. Such effects can be minimized by increasing the probing beam energy as the channeling critical angle is inversely proportional to the square root of the incident energy. Hence small angular misalignments can also be resolved in the high energy channeling experiments. Heavy ions are chosen so as to have reasonably high scattering cross‐section and also to avoid the nuclear react...