Laser Assisted Molecular Beam Deposition of High Mobility Zinc Oxide

Abstract

ABSTRACTWe have utilized laser assisted molecular beam deposition (LAMBD) to deposite zinc oxide (ZnO) at room temperature. The production of ZnO films via LAMBD utilizes an excimer laser induced ablation plume of zinc in combination with pulsed oxygen gases to create a molecular beam of ZnO clusters. The deposited films have been characterized structually and electrically in an as deposited state as well as after post deposition excimer laser annealing. The films undergo a clear structural change from a nanoparticle like film to either a microgranular film or a smooth continuous film depending upon the laser annealing power.Al ohmic contacts were made to both as-deposited and laser-annealed ZnO thin films. Thickness and refractive index, chemical composition, and surface morphology of the thin films were analyzed by using ellipsometry, electron spectroscopy for chemical analysic (ESCA), and feild emission scanning electron microscopy (FESEM), respectively. Dark current-voltage (I-V), DC photo I-V, Hall-effect, and photoluminescence measurements were employed for testing the device performance.In some cases, the ZnO thin film was changed from n-type into p-type after laser annealing, and photoconductive behavior was clearly seen on the laser-annealed samples, with values of 2.8 × 10−4 Ω−1. Also, both samples with and without laser annealing show near-band emission at ∼3.3 eV. Furthermore, the full width at half maximum (FWHW) values of the laser-annealed LAMB ZnO film was reduced from 20.02 nm or 21.68 nm to 18.2 nm when compared with that of non-laser annealed samples. This indicates that the laser annealing provided an improved stochiometric quality and crystallinity to the ZnO thin films.