Growth And Properties Of GaN And InN Films Prepared By ECR-PEMOCVD

Due to their great potential use in optoelectronic and microelectronic devices, GaN-based III nitrides semiconductor materials have been widely investigated. In 2002, it has been reported that the optical band gap of InN is 0.7eV, not the commonly quoted value 1.89 eV. This means that the band gap of InxGa1-xN ternary alloy can be continuously tuned from 3.4eV (GaN) to 0.7eV (InN). by adjusting the In fractions. The corresponding absorption spectrum can be stretched from the ultraviolet part (366nm) to nearly infrared part (1771nm), covering almost the whole solar absorption spectrum. It is predicted that the efficiency of the InGaN tandem solar cell can be up to 72%. Therefore, study on the InGaN solar cell will be of great value.In order to obtain high efficiency InGaN solar cell, it is essential to prepare high-quality InGaN films in which the In fractions can be tuned. However, it requires the preparation of high-quality GaN and InN films at the first step.The experiments were carried out on the Electron Cyclotron Resonance-Plasma Enhanced Metal Organic Chemistry Vapor Deposition (ECR-PEMOCVD) system equipped with in-situ Reflection High Energy Electron Diffraction (RHEED). The experiments were classified into two parts:1. Using trimethyl-gallium(TMGa) as Ga source, high purity N2 as N source, GaN films were deposited on ZnO:Al layer; 2. Using trimethyl-indium(TMIn) as In source, high purity N2 as N source, InN films were deposited onα-Al2O3 substrate.The crystal structure and surface topography of the films were characterized by RHEED, x-ray diffraction (XRD) and atomic force microscope (AFM). The electrical properties of the films were investigated by Hall measurements. The lattice vibration was characterized by Raman spectra.GaN films deposited at 200～500℃are of high c-axis preferred orientation and have good crystalline characteristic. The surface morphology of GaN films is smooth. The optical transmittance and band gap at the optimal growth temperature is 85～90% and 3.45 eV, respectively.InN films deposited at the temperature range of 350～550℃and a TMIn flux range of 0.4～1.0 sccm exhibited high (0002) preferred orientation and good wurtzite-type structure. Raman studied showed that there are significant A1 (LO) and E2 (High) models. The room temperature carrier mobility rate is 10～40cm2/v·s, and sheet concentration is about 1016 obtained by Hall measurement.