The Surface Of GaSb_1-xBi_x And Interface Of InGaAs/InP Studied By Scanning Tunneling Microscope

Ultra-high vacuum scanning tunneling microscope(UHV STM)is an important characterization technique for studying topography and structure of semiconductor surfaces.It also has the function of scanning tunneling spectroscopy(STS),which provides directly the local electronic structure information.In this thesis,we used this advanced characterization tool to study two important III-V materials grown by molecular beam epitaxy(MBE),GaSb_1-xBi_x and InGaAs/InP heterojunction.GaSb_1-xBi_x,a new type of dilute bismuth semiconductor,has attracted a broad attention due to its application prospect for 2-4 ?m mid-infrared lasers and photodetectors.Its optimal growth is still under investigation.An important issue involved is how to solve the conflict between the effectively doping of Bi atoms and improvement of crystal growth quality.It is an indispensable content to assess the quality of material with the optimization of growth conditions.The morphology characterizations may provide deep understanding on the growth dynamics.Based on collaboration with the MBE growth group of the Shanghai Institute of Microsystem and Information Technology,the thesis had used UHV STM characterized systematically the GaSb_1-xBi_x films with the different growth conditions.InGaAs/InP avalanche photodiode(APD)structure is the other material studied by the thesis,which has attracted great attention with the development of single-photon detection technology.The structure is also grown by epitaxial growth method.Since the property of interface is important to the performance of device,but there is few effective characterization method,the cross-section STM(XSTM)is one of typical methods for characterization.The XSTM was conducted to explore the heterojunction structure.The main content includes:1.We used STM to characterize the pristine GaSbBi film of 200nm grown at low temperature.We observed different types of cross-hatch pattern morphology.For the etched sample surface,we inferred that the cross-hatch patterns originate from different crystal plane tilting during the growth process.In addition,we also compared GaSbBi samples with high Bi content obtained by changing the Bi/Sb flux ratio during MBE growth.We found that the sample quality with high Bi content declines.The STS measurement showed that the surface generally displays metallic characteristics.2.We observed the original GaSbBi surface with thickness of 5nm and l0nm by STM.Comparing the morphologies of the two samples,we inferred that the few-layer growth mode is Stranski-Krastinov(SK)mode,i.e.a two-dimensional growth followed by the three-dimensional growth consequently.And it will eventually transition to Volmer-Weber(VW)mode,i.e.three-dimensional island growth.3.Different from STS measurement result of thick epitaxial surface,the few layer STS results clearly showed the energy band gaps of the material.A statistical analysis on the spatial distribution of STS results was conducted to reveal the inhomogeneity spatial distribution of the electronic structure.It showed that the increasing on the thickness of the sample increases not only the incorperation of Bi but also increases the spatial inhomogeneity of the electronic structure.4.The InGaAs/InP APD heterojunction structure was characterized by using cross-section STM(XSTM).The cleaved interface of InGaAs layer and InP substrate displayed atomic flat terraces,but the interface adjacent to InGaAs showed different cleaved morphology.The observation implied that the spatial inhomogeneity of the interface stress during cleavage as a significant impact on the cleavage effect.STS showed that the tip induced band bending(TIBB)effect on InP and InGaAs was different of which the TIBB causes the measured apparent band gap of InGaAs be significantly larger than its intrinsic band gap.