The magnetic field induced metal insulator transition in doped semiconductors will be investigated by combined transport and far infrared spectroscopic measurements. The transport measurements will be used to determine the critical field for the metal insulator transition and to investigate interaction and weak localization effects in the metallic state and the activated conductance in the insulating state. The spectroscopic measurements will be used to investigate the electronic structure of the systems away from the Fermi energy. The transformation of the cyclotron resonance and spin resonance signals on the metallic state to the impurity transitions in the insulating state will be investigated. These studies are on materials of importance to high speed opto-electronics. This program is a collaborative effort between Professor Shayegan at Princeton Professor Drew at Maryland. These studies are on materials of high technological importance and related to high speed opto-electronics.