Temperature-dependent relaxation and growth phenomena in strained InxGa1-xAs layers grown on GaAs.

Abstract

A series of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs layers with x ranging from 0.36 to 1 was grown by molecular-beam epitaxy, in order to examine the dependence of the critical layer thickness (CLT) on the In mole-fraction and growth temperature. Reflection high-energy electron diffraction (RHEED) and photoluminescence (PL) measurements were used and indicated a reduced CLT with increasing substrate temperature. A large difference in CLT was found between layers examined by RHEED and PL. This is discussed and explained to be a consequence of the difference in layer structure between layers examined by PL and by RHEED. While RHEED is a surface sensitive method, the luminescence in PL experiments originates from embedded layers. In PL measurements the thickness of the onset of three-dimensional growth, ${\mathit{t}}_{3_{\mathrm{D}}}$, decreased from 55 to 15 \AA{} for ${\mathrm{In}}_{0.36}$${\mathrm{Ga}}_{0.64}$As layers as the growth temperature increased from 470 to 570 \ifmmode^\circ\else\textdegree\fi{}C. The PL study also indicated a reduced temperature dependence with increasing In content. The RHEED measurements for ${\mathrm{In}}_{0.36}$${\mathrm{Ga}}_{0.64}$As showed that the thickness when the surface lattice parameter becomes equal to that of the alloys varied from 95 to 10 \AA{} for growth temperatures between 490 and 590 \ifmmode^\circ\else\textdegree\fi{}C, respectively. Calculations by the most frequently used models for estimating the CLT were also carried out. The model of Price [Phys. Rev. Lett. 66, 469 (1991)] best fits our experimental results. The carrier mobility in 2-\ensuremath{\mu}m-thick InAs layers was measured between 20 and 300 K for layers grown at substrate temperatures between 390 and 525 \ifmmode^\circ\else\textdegree\fi{}C. The results indicate a peak mobility of 17 266 ${\mathrm{cm}}^{2}$/V s at 300 K for a structure grown at 520 \ifmmode^\circ\else\textdegree\fi{}C and a peak mobility at 77 K of 34 000 ${\mathrm{cm}}^{2}$/V s for a sample grown at 510 \ifmmode^\circ\else\textdegree\fi{}C.