In situ Study of Strain Relaxation Mechanisms During Lattice-mismatched InGaAs/GaAs Growth by X-ray Reciprocal Space Map
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1268-EE06-02
In situ Study of Strain Relaxation Mechanisms During Lattice-mismatched InGaAs/GaAs Growth by X-ray Reciprocal Space Mapping Takuo Sasaki1, Hidetoshi Suzuki1, Akihisa Sai1, Masamitu Takahasi2, Seiji Fujikawa2, Yoshio Ohshita1, Masafumi Yamaguchi1 1
Semiconductor laboratory, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku,
Nagoya 468-8511, Japan. 2 Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo 679-5148 Japan.
ABSTRACT The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study. INTRODUCTION Understanding of strain relaxation mechanisms during III-V lattice-mismatched heteroepitaxy is necessary to achieve high-quality optoelectronic devices with long operational lifetime. In mismatched heteroepitaxy, the structure of the buffer layer is particularly important, as it reduces the defect densities in the film and improves the quality of crystal grown on a substrate. By adopting appropriate relaxed buffer layers, the dislocation densities in mismatched semiconductors can be decreased, enabling photovoltaic cells with high performance to be realized. While extensive experimental studies have been performed to investigate the strain relaxation mechanisms, in situ measurements are more promising for understanding details of the strain relaxation process without the influence of the thermal strain due to difference in thermal expansion coefficients of substrate and epitaxial layer. Recently, we have successfully developed in situ X-ray reciprocal space mapping (in situ RSM) during lattice-mismatched InGaAs/GaAs(001) growth to observe the residual strain and crystal quality simultaneously, and investigate the dislocation mediated strain relaxation.1 A number of analytical models on a strain
relaxation have also been developed to explain the variation of the residual strain in partially relaxed layers from equilibrium2 to kinetic approaches. Dodson and Tsao developed a kinetic model that included a phenomenological model for the dislocation multiplication and empirical model for dislocation glide velocity in a strain field.3 Their model has been applied to a number of heteroepitaxial systems, in an attempt to better understand strain
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