OPTICAL SPECTROSCOPY OF CARRIER RELAXATION AND TRANSPORT IN III/V SEMICONDUCTOR TUNNELING STRUCTURES

摘要

Since the proposal and the demonstration of carrier tunneling in III/V semiconductor heterostructures, there has been a considerable and persistent interest in these phenomena. One motivation is the investigation of fundamental physical principles of quantum tunneling, and in a detailed description in the case of its realisations using semiconductor materials. This has direct relevance for the understanding and improvement of related systems, e.g., the intersubband infrared lasers also called quantum cascade lasers. On the other side there are perspectives for application of semiconductor tunneling structures in a variety of practical electronics devices including ultrahigh-speed devices oscillators, multi-valued logic switches, fast A/D converters and special purpose light-emitting diodes. The highly nonlinear I-V characteristics with eventual negative differential resistance (NDR) is an essential ingredient for most of the proposed applications. From the late eighties on, both steady-state and time-resolved photoluminescence were applied to investigate charge build-up near and inside a quantum well (QW) , the escape of electrons and holes from quantum wells, including partial results for unipolar devices under applied bias . In this paper, we will give an overview of the results we obtained since then by optical spectroscopy in different III/V tunneling structures. Some of the device-oriented aspects have already been discussed previously. Here, we will first consider unipolar double-barrier (DB) and triple-barrier (TB) resonant tunneling structures (RTS), in which tunneling times of minority-carrier have been determined. Then, bipolar devices are discussed with either a RTS or only a single barrier in the junction region, the so-called called RTLED (resonant tunneling LED), and TLED (tunneling LED) devices, respectively. Besides detailed understanding of carrier transport and electrical and optical phenomena, these investigations have also led to the design of electro-optic devices with ultrafast switching characteristics which are presently under further investigation.