| Photoconductivity effects of undoped semi-insulating gallium arsenide is studied, from which the material can be characterized using microwave reflection techniques without making any contact. A photoconductivity model, consisting of a deep donor level EL2 and a shallow acceptor level, is proposed and used to explain the above-band-gap (ABG) and below-band-gap (BBG) transient and steady state photoconductivity response. The use of microwave reflection techniques allows a contactless characterization of resistivity, shallow acceptor (carbon) concentration, and deep levels of SI-GaAs materials.;The measurement performed using microwaves essentially provides two important pieces of information of semiconductors: conductivity and lifetime. In order to evaluate quantitatively the conductivity induced by a monochramatic light the choke-flange rectangular waveguide is used as a probing element. When a SI-GaAs wafer backed by a metallic short is placed near to the open-end of the choke-flange rectangular waveguide the electromagnetic field distribution can be assumed to be TE;During the course of this study we have used more than 20 LEC-grown undoped SI-GaAs wafers, with carbon concentration ranging from less than 3 ;The BBG transient microwave response shows an initial fast decay after the light is turned off which can not be explained by using the photoconductivity model. In order to explain the initial fast decay an additional deep donor level is incorporated into the photoconductivity model which is studied at different temperatures.;A new characterization technique, called photoinduced microwave deep level transient spectroscopy PMDLTS, is introduced and demonstrated to be capable of detecting deep levels in ion-implanted SI-GaAs materials. However, in bulk SI-GaAs wafers no deep level was found to be above the EL2 by using this technique. |
