MOVPE growth and characterization of ZnSe based materials for short-wavelength multiple quantum well optical modulator applications

This thesis describes a detail study of growth of high quality ZnSe based epitaxial materials co-doped with Cd and Cl. These films have been grown on GaAs substrates under high temperature as well as under ultraviolet (UV) photo-assisted low temperature using metalorganic vapor-phase-epitaxy (MOVPE) technique. The influence of temperature and UV intensity on the optical characteristics and surface morphology of these epitaxial films has been investigated. It is found that more intense near-band-edge emission (NBE) is observed when the growth temperature is reduced. The films grown under high temperature shows strong undesired deep-level emission (DLE). This deep-level emission shows a threshold-like dependence on the UV light intensity for a given temperature. The ZnSe films grown under UV photo-assisted low temperature conditions exhibit much higher optical quality when the growth temperature is reduced from 600°C to as low as 350°C. The near-band-edge emission to deep-level emission ratio is greatly improved by a factor of at least 350. ^ The n-type ZnSe epitaxial films have been grown using HCl as a dopant. The factors that influence the n-type Cl-doping level have been studied in detail. Using Cd as a co-doping dopant, the Cl doping level can be increased significantly. With co-doping of Cd the electron concentration of 2.45 × 1018 cm−3 is obtained by Hall Effect measurement, the highest n-type doping reported using HCl by MOVPE to our knowledge. ^ The Zn1−xCdxSe ternary compound epitaxial films have also been grown using low temperature UV photo-assisted method. The desired ternary Zn0.8Cd0.2Se compound films that can be used for quantum well structure applications were obtained. The influences of growth temperature, UV intensity, and gas flow ratio on Cd composition control have been intensively studied. It is found that the Cd composition is very sensitive to these parameters. This thesis also presents simulation results involving optical transmission characteristics of a ZnCdSe/ZnMgSSe multiple quantum well optical modulator. ^ Several papers have been published in different journals based on the results presented in this work. They are attached as an appendix.