Exciton recombination energy in spherical quantum dots on Ga_(1-x)In_xAS_ySb_(1-y)/GaSb grown by liquid-phase epitaxy

摘要

Photoluminescence and photoreflectance responses at 12 K of Ga_(1-x)In_xAS_ySb_(1-y) films grown over GaSb single-crystal substrates by liquid-phase epitaxy do not exhibit the same energy values. The photoluminescence peak shifts to 20 meV in relation to the photoreflectance response, indicating a possible electronic confinement in some parts of the growth heterostructure. The possibility of low-dimensional structures is investigated herein. They are possibly formed during the growth process and are responsible for this energy shift. The optical emission spectra associated with transitions between the first conduction and valence-band levels in spherical Ga_(1-x)In_xAS_ySb_(1-y)/GaSb quantum dots, using x and y values in the range of 0.11-0.15 and 0.10-0.14, respectively, are studied here. These ranges were chosen according to experimental results obtained from the samples under study. Spherical potential wells of finite depth determined by the discontinuity in the conduction band ΔE_C for electrons and the discontinuity in the valence band ΔE_v for holes were used. In the calculations, the variational procedure within the effective-mass approximation was used and electrons and holes in a type-I band alignment formed by two semiconductors with similar parabolic conduction bands were considered. From these results, it was concluded that higher electronic confinements such as quantum dots were possibly formed during the growth process in some areas of the heterostructure.