Microscopic characterization of ${\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{0.28}{\mathrm{GaSb}}_{0.72}/\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{S}\mathrm{b}$ laser structure interfaces

We have used cross-sectional scanning tunneling microscopy (XSTM) and transmission electron microscopy (TEM) to study ${\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{0.28}{\mathrm{Ga}}_{0.72}\mathrm{S}\mathrm{b}/\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{S}\mathrm{b}$ strained-layer heterostructures designed for use in infrared lasers. The samples came from the same material previously characterized by photoluminescence (PL) and x-ray diffraction [M. J. Yang et al., J. Appl. Phys. 86, 1796 (1999)]. Several structures grown at different temperatures and with either III-As or III-Sb-like interfacial bonds have been characterized. Analysis of high-resolution TEM images finds the same degree of interfacial roughness (∼1 ML) for both III-As and III-Sb interfacial bonded heterostructures, despite significantly greater PL intensity in the latter. We also implement and compare two different methods for analyzing the interfacial roughness using XSTM; both show that the crucial InAs/InGaSb interface is rougher in the samples grown at high temperature. Even in samples grown at the optimal temperature (∼440 °C), XSTM reveals intermixing at the AlSb-on-InAs interfaces, as well as unexpected differences in the interfacial bond types at the InAs-on-AlSb vs AlSb-on-InAs interfaces. Whereas all layers grown at or below the optimal growth temperature appear defect-free in TEM, threading dislocations are observed in samples grown at higher temperature.