Scanning tunneling microscopy studies of nano-scale properties of III/V semiconductor heterostructures

The nanometer-scale structure of heterojunction interfaces and of alloy layers in III/V semiconductor heterostructures can directly and profoundly influence material properties and device performance. Interfacial roughness will reduce carrier mobility, and interfacial abruptness will affect carrier confinement. Various forms of compositional variations have been observed to occur in a wide variety of III/V alloys and can have a major impact on material properties. Atomic- to nanometer-scale characterization of interface and alloy layer structure in III/V heterostructures is, therefore, very important for optimization of material properties and device performance.; STM is an extremely powerful tool for atomic-scale characterization of heterostructure interfaces and compositional structure in alloys, due to its high sensitivity to electronic structures and its extremely high spatial resolution. In this dissertation, results of several cross-sectional scanning tunneling microscopy (STM) studies performed on a variety of phosphide, arsenide, and antimonide III/V semiconductor heterostructures are presented.; Fourier analysis of interface roughness observed in STM images of Ga _1−xIn_xSb/InAs heterostructures is performed, showing an anisotropy in interface roughness and the dependence of interface roughness on growth sequence. STM characterization has been performed on InAsP(N)/InP, InAs_xSb_1−x/InAs_yP_1−y/InAs, and GaAs_1−xSb_x/GaAs heterostructures. Within InAsP(N)/InP multiple-quantum well (MQW) samples, STM characterization reveals that As-rich clusters are present within the alloy layers, possessing triangular (110) cross-sections and elongated along the [110] direction. STM contrast also shows that N incorporation into the InAsP layer will increase the valence band offset of InAsP(N)/InP heterostructure. Within InAs_xSb _1−x/InAs_yP_1−y MQWs, compositional features oriented along ⟨112⟩ direction in the (110) cross-section have been observed in STM images. Moreover, the ⟨112⟩ compositional features, which are associated with an average lattice constant differing from that in surrounding materials, appear to be aligned across the InAs_xSb_1−x/InAs_yP_1−y interfaces, suggesting that strain plays an important role in the formation of such structures. For GaAs_1−xSb_x/GaAs samples, STM images reveal nanometer-scale compositional variations within the alloy layer and the effect of group V interface soaks on interface roughness and abruptness. A detailed methodology is developed for strain analysis, which reveals quantitative nanoscale compositional profile within the alloy layer.