Fabrication of closely spaced quantum dot diodes

Abstract

Quantum dot devices have been proposed as the basic structure for an integrated circuit technology with extremely high functional density [R. T. Bate, Sci. Am. 258, 96 (1988)]. Electronic transport has been reported through quantum dot diodes which are resonant tunneling devices with lateral dimensions small enough to produce zero-dimensional (0D) confinement effects [M. A. Reed, J. N. Randall, R. J. Aggarwal, R. J. Matyi, T. M. Moore, and A. E. Wetsel, Phys. Rev. Lett. 60, 535 (1988); G. Faini, A. Ramdane, F. Mollot, and H. Launois, (to be published) NATO Workshop Spain 1990; S. Tarucha, Y. Hirayama, T. Saku, and T. Kimura, Phys. Rev. B 41, 5459 (1990)]. We seek improvements in the switching characteristics of these 0D tunneling devices as well as processing techniques to fabricate them very close together in an attempt to study field coupling between dots. We will discuss the processing issues involved with fabricating very closely spaced quantum dot diodes. We are building pairs of quantum dot diodes which are approximately 1500 angstroms in diameter and spaced a few hundred angstroms apart. e-beam lithography is used to define the dot patterns. The use of nonalloyed InGaAs contacts, which is essential to providing ohmic-type contacts of this small diameter, [J. N. Randall, C. H. Yang, Y. C. Kao, and T. M. Moore, J. Vac. Sci. Technol. B 7, 2007 (1989); P. Gueret, P. Buchmann, K. Daetwyler, and P. Vettiger, Appl. Phys. Lett. 55, 1735 (1989)], presents complications for the reactive ion etching of these structures. The task of independently contacting two very small and closely spaced contacts requires high resolution lithography and accurate re-alignment techniques. The e-beam lithography techniques used to accomplish this task will be presented. Finally some transport measurements through isolated quantum dot diodes will be presented.