In situ processing of quantum structures using focused ion beam implantation and molecular beam epitaxy growth and regrowth.

摘要

We have developed in situ processing techniques using a UHV focused ion beam (FIB) together with a molecular beam epitaxy (MBE) system to achieve several processing sequences (including regrowth and local doping) that are useful for quantum structures. First, the processing conditions (ion energy, dose, growth conditions and annealing conditions) were systematically investigated to improve the quality of the regrown layer, and to understand the mechanism of defects generation and propagation in the regrown layers; secondly, three device structures were fabricated based on the development of the in situ process technique, and the physical properties of these structures were investigated.; The quality of the regrown QWs over the implanted surface is affected by (1) the point defects propagation during RTA, (2) amorphization and (3) interface roughness induced by ion implantation. Low dose and high energy implantation are two key factors to form good quality regrown QWs. In situ rapid thermal annealing prior to regrowth would be necessary to completely remove the ion implantation induced damage and to achieve high quality QWs. Good quality 2DEGs with a mobility up to 17000 cm{dollar}sp2{dollar}/Vs and a carrier concentration of 2.2 {dollar}times{dollar} 10{dollar}sp{lcub}11{rcub}{dollar}/cm{dollar}sp2{dollar} were formed in the inverted AlGaAs/GaAs interface. Interface roughness and vacancies are probably the main scattering mechanism at low temperature in the regrown quantum wells.; A buried stressor structure that produces a lateral band gap modulation in GaAs/AlGaAs quantum well was demonstrated. CL measurements showed that a 12 meV potential well for exciton was formed. The measured band gap shrinkage was found in agreement with the theoretical calculations.; The basic characteristics of the inverted HEMT were demonstrated. Good quality resonant tunneling diodes (RTD) were demonstrated on the Si FIB implanted surface and regrown structures. The peak to valley ratio of this device was 3 at room temperature and 10 at 77 K, indicating the performance of the RTD is comparable to that of structures made directly by MBE. Exploratory work on novel device structures using this in situ processing has been started, for example, ultra small emitter RTD structures that show a low temperature fine structures in their I-V characteristics have been made. (Abstract shortened with permission of author.)