Using the di-vacancy hopping model to analyse Ge out-diffusion and its effect on ordering phase in InGaP grown on Ge substrate
Date Issued
2016
Date
2016
Author(s)
Wu, Hong-Ming
Abstract
We report on the structural properties of ordering InGaP directly deposited on (001) Ge substrate by organometallic vapor phase epitaxy. The Ge substrate is 6° miscut towards (110). Results from transmission electron diffraction indicate the existence of CuPt-B ordering phase in the sample. The ordering direction is assigned to be [1-11], which is perpendicular to the miscut direction of the Ge substrate. Because only one ordering phase is observed, no anti-phase domain exists in the sample. The order parameter determined from photoluminescence at room temperature is 0.47. Raman scattering was also used to analyze the ordering effect. A mode at 354 cm-1 relevant to the ordering phase confirms that the CuPt-B ordering is along [111]. We study Ge auto-doping and out-diffusion in InGaP epilayer with Cu-Pt ordering grown on 4-inch. Ge substrate. Ge profiles determined from secondary ion mass spectrometry indicate that the Ge out-diffusion depth is within 100 nm. However, the edge of the wafer suffers from stronger Ge gas-phase auto-doping than the center, leading to ordering deterioration in the InGaP epilayer. In the edge, we observed a residual Cu-Pt ordering layer left beneath the surface, suggesting that the ordering deterioration takes place after the deposition rather than during the deposition and In/Ga inter-diffusion enhanced by Ge vapor-phase auto-doping is responsible for the deterioration. We thus propose a di-vacancy diffusion model, in which the amphoteric Ge increases the divacancy density, resulting in a Ge density dependent diffusion. In the model, the In/Ga inter-diffusion and Ge out-diffusion are realized by the random hopping of In/Ga host atoms and Ge atoms to di-vacancies, respectively. Simulation based on this model well fits the Ge out-diffusion profiles, suggesting its validity. By comparing the Ge diffusion coefficient obtained from the fitting and the characteristic time constant of ordering deterioration estimated from the residual ordering layer, we found that the hopping rates of Ge and the host atoms are in the same order of magnitude, indicating that di-vacancies are bound in the vicinity of Ge atoms. Finally, we compare of the Ge gas phase auto-doping and out-diffusion in InGaP epilayers grown on 4-inch with and without Si3N4 coating on backside of Ge substrate by organometallic vapour phase epitaxy. The edge of the wafer suffers from stronger Ge gas-phase auto-doping than the centre, which increase Ge atoms incorporate of initial GeIII and GeV and leading enhancement of out-diffusion. In SIMS auto-doping region indicate the Si3N4 capping backside sample reduces the most of all gas phase auto-doping, but only substrate wafer side uncapping. This result leading to auto-doping region present exponent decay profile in SIMS. In the with and without edge sample, we observed a residual Cu-Pt ordering layer left beneath the surface, suggest that the deteriorating of the ordering takes place after the deposition. We used di-vacancy diffusion model and added exponent decay of gas-phase auto-doping, in which the amphoteric Ge increases GeV/GeIII compensation ratio and promotes In/Ga inter-diffusion with increasing the di-vacancy density. Simulation based on this model well fits the Ge out-diffusion profile in the both sample, suggesting its validity. In edge sample, with coating sample of PL energy different of two peak is close than without sample. It attribute decrease of gas-phase auto-doping and enhancement uniformity of degree of order in depth of epilayer. These findings are obviously in consistent with that obtained from the Di-vacancy model.
Subjects
Di-vacancy hopping model
out-diffusion
inter-diffusion
ordering
Type
thesis
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