Resonant tunneling of double-barrier quantum wells affected by interface roughness.

Abstract

Resonant tunneling of double-barrier quantum wells (DBQW's) affected by interface roughness has been investigated. Our results show that interface roughness induces oscillation resonant structure around the principal resonant peak. EA'ects of interface roughness on the resonant bias voltage, peak-to-valley current ratio, and the width of the principal resonant peak are also investigated. Temperature eAect is discussed. The results obtained here may be used to explain the oscillation or intrinsic instability observed in DBQW resonant-tunneling structures. With recent developments in semiconductor artificial structures, such as quantum wells (QW's) and superlattices (SL's), many important physical properties have been explored. In fundamental physics, quantum-well and superlattice structures have been used to explore the physical properties of low-dimensional systems and quantum efFects. Many novel phenomena in the quantum regime have been discovered, such as resonant tunneling of double-barrier quantum wells with negative differential resistance. ' Applications of these quantum wells and superlattices include high-speed electronics, photoelectronics, and photonic devices such as quantum-well lasers, modulation-doped field-effect transistors (MODFET's), photodetectors, etc. Double-barrier quantum-well (DBQW) tunneling structures have recently drawn a great deal of attention because tunneling is the fastest charge-transport phenomenon in semiconductors. Many important properties of resonant tunneling of electrons in DBQW's have been observed, such as negative differential resistance. Although many important properties of DBQW tunneling structures have been discovered, there are still many important questions to be answered, such as those concerning oscillation or instability in DBQW resonanttunneling structures. Although molecular-beam-epitaxy (MBE) can be used to fabricate the quantum-well or superlattice structures on an atomic scale, interface roughness cannot be cornpletely eliminated. It is important to understand how this interface roughness afFects the transport properties of DBQW structures. In some cases the presence of interface roughness simply acts as a small perturbation on effects that already exist in the absence of interface roughness. In other cases it can lead to quantitative changes in phenomena that exist in the absence of interface roughness. An example of this would be the roughness-induced splitting of the surface-plasmon dispersion curve observed experimentally, and discussed theoretically. Overall, roughness can have a significant influence on effects occurring at interfaces. The effects of interface roughness on the optical properties of quantum wells have been studied previously. The dominant effects observed due to interface roughness were the exciton linewidth broadening and the Stokes shift of the emission: the emission of the lowest heavyhole exciton generally is slightly shifted to lower energy (typically a few millielectron-volts) with respect to the absorption- or excitation-spectrum maximum. Recently, dynamic processes of excitonic transitions affected by interface roughness have also been studied. The excitontransition peak shifting towards lower energy with increasing delay time caused by interface roughness has been observed. In this paper, effects of interface roughness on the resonant tunneling in DBQW structures have been investigated. We show that interface roughness can cause multiple resonance peaks in DBQW's, and thus strongly modify the I- V characteristic. The I- V characteristic for different interface-roughness parameters as well as for different DBQW structures are studied. The effects on multiple resonance peaks are discussed. From our results, it is possible that the previously observed oscillations between the low- and high-current states in the DBQW s (Ref. 5) or intrinsic instability is induced by interface roughness.