TRAP BEHAVIOR IN NONINTENTIONALLY DOPED ALGAAS/GAAS SINGLE QUANTUM-WELL STRUCTURES

The GaAs/AlGaAs single quantum well (SQW) samples with nonintentionally doped confining layers were studied using deep level transient spectroscopy (DLTS) and capacitance-voltage-temperature. A sizeable DLTS signal was observed and believed to be from the thermal emission of the well electrons. However, it was found that the major signal peak was accompanied by two subpeaks and thus the QW must be a multilevel trap state. Different combinations of reverse voltage and fill pulse height allowed a DLTS study of the region before, within, and beyond the well location. Such an observation, in conjunction with the use of undoped AlGaAs barrier layers, proved that the DLTS signal is indeed from the well because it was only significant when probed within the well region and the assumption of the DX centers in some previous studies can be excluded. The fact that classically derived activation energy is close to the estimated band-gap discontinuity value and the carrier distribution centered at the geometric QW at room temperature revealed that the quantization effect was of second order. However, the detected activation energy depends on the testing conditions that precludes the determination of the band offset using the DLTS technique.