Investigation of charge transport confined at a heterojunction along the junction plane by Monte Carlo tecniques

ABSTRACT PhD. THESIS INVESTIGATION OF CHARGE TRANSPORT CONFINED AT A HETERO JUNCTION ALONG THE JUNCTION PLANE BY MONTE CARLO TECHNIQUES Zeki YARAR DEPARTMENT OF PHYSICS INSTITUTE OF NATURAL AND APPLIED SCIENCES UNIVERSITY OF ÇUKUROVA Supervisor: Assoc. Prof. Metin ÖZDEMİR Year: 2004, Pages: 165 Jury: Assoc. Prof. Metin ÖZDEMİR : Prof. Ramazan ESEN : Prof. Halil YARANERÎ : Prof. Gttlten GÜNEL : Prof. Yusuf ÜNLÜ Schrödinger and Poisson equations are solved self consistently to obtain the potential profile formed at a modulation doped AlGaAs/GaAs hetero junction. In addition empty or occupied quantized energy levels, charge carrier concentrations in each occupied level, wave functions corresponding to each level are also calculated. No adjustable parameters are used, it is sufficient to provide only the material parameters. Armed with the information given above, electron scattering rates based on Born approximation are calculated using a combination of analytical and numerical methods. The scattering mechanisms considered are: surface roughness, acoustic phonon, polar optic phonon and remote impurity scattering. Assuming that the two-dimensional electron concentration is not altered, the variation of chemical potential with respect to both temperature and energy level-broadening parameter is studied under a uniform and constant magnetic field. Gaussian, exponential and lorentzian forms of broadening are used and the results are compared. Then using ensemble Monte Carlo method, the drift velocity of electrons along the hetero junction plane, the variation of low field mobility of electrons at the hetero junction, the occupancy of the quantized sub bands and three dimensional valleys are obtained as a function of applied electric field at various temperatures and material parameters. The temperature and/or field beyond which two dimensional nature of the system ceases to exist is also investigated. Similar calculations are repeated for a quantum well. In both cases, emphasis is given to the effect of surface roughness and remote impurity scattering on electron transport properties and electron mobility. Key Words: Scattering, self-consistent, Monte Carlo, mobility, chemical potential. II