Investigation of InAs quantum dots grown on the Ge substrate without migration enhance epitaxy layer

Abstract

Properties of self-assembled III-V quantum dot (QD) heterostructures for optoelectronic devices mainly rely on growth parameters and also on substrate used. The research community mainly preferred GaAs substrate instead of Si substrate for optoelectronics. However, the low cost and abundance of Si impels the researchers and industrialists to use Si for the commercial application using SixGe1-x graded layer and Migration Enhanced Epitaxy (MEE) layer. Here we have studied the optical and structural study of Stranski–Krastanov (S-K) InAs quantum dots grown on Ge substrate with 6° offcut toward the (110) plane (Sample A) without MEE layer, which may be easy to integrate on Si. Starting from the thick GaAs buffer layer, AlAs/GaAs super-lattice buffer layers followed by three consecutive layers of 2.7 ML S-K InAs QDs with 50 nm GaAs capping were grown. Another sample (B) with the same heterostructure was grown on GaAs substrate for comparison. Low temperature photoluminescence (PL) for the sample (A) is blue-shifted as compared to sample B, which might be due to smaller dots formation. The bi-modal dot size distribution of the sample A and sample B was confirmed from the power dependent PL. In the low temperature PL spectrum, full width half maxima (FWHM) of the sample A is very close to that of the sample B. Rocking curve obtained from high resolution X-ray diffraction (HRXRD) for the sample A, shows Ge substrate peak and GaAs peak from the GaAs layer grown on the Ge substrate. The strain calculated from the HRXRD rocking curve for the sample A and sample B is -4.12x10-3 and -2.0x10-3 respectively. Strain value indicates crystalline quality of sample A is good and comparable to the same in sample B, grown on the GaAs substrate. The optical properties for the sample A can be enhanced further via monolayer coverage of the dots, capping material, capping thickness and ex-situ annealing techniques.