Optical reading of InGaAs modulation doped field effect transistor

The first observation of absorption quenching in a semiconductor quantum well by electrical control of the carrier density is presented. This novel effect was observed at room temperature in a single modulation doped InGaAs quantum well which was used as the conducting channel of a field effect transistor (FET). The effect is extremely large and it was used for direct optical determination of the state of the FET. Modulation doping (MD) can be used to introduce carriers in QW, producing very high mobility materials well known for their application to high speed transport. Because the carriers fill the two dimensional subbands up to the Fermi energy, the absorption edge is blue shifted with respect to the luminescence emission, with a shift approximately proportional to the number of carriers. Thus electrically driven changes of the carrier density in a MD-QW will result in large changes in optical absorption. The conditions for the observation of this phenomenon correspond exactly to the situation encountered during the switching of a FET whose conducting channel is a MD-QW.