Growth, Characterization, and Simulation of Novel Semiconductor Tunnel Structures

Citation

Chow, David Hsingkuo (1989) Growth, Characterization, and Simulation of Novel Semiconductor Tunnel Structures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/96gc-kc14. https://resolver.caltech.edu/CaltechETD:etd-11212003-115412

Abstract

This thesis presents investigations of novel semiconductor heterostructure devices based on quantum mechanical tunneling. Due to their small characteristic dimensions, these devices have extremely fast charge transport properties. Thus, it is expected that tunnel structure devices will be well-suited to high frequency and optoelectronic applications. The work presented here can be divided into three sections. In the first section, a theoretical model for simulating current-voltage behavior in single barrier heterostructures is developed. The simulations are then used to design a novel single barrier negative differential resistance (NDR) device. The second section consists of detailed experimental characterizations of single barrier Hg_1-xCd_xTe heterostructures, including the first demonstration of the novel single barrier NDR mechanism. Growth of III-V semiconductor heterostructures by molecular beam epitaxy (MBE) is the subject of the third section. Several aspects of tunneling are explored through characterization of these III-V structures.

In chapter 2, a theoretical model is developed to simulate tunneling currents in single barrier heterostructures. The model includes band bending effects and a two band treatment of electron attenuation coefficients in the barrier. It is proposed that certain material systems have the appropriate band alignments to realize a novel single barrier negative differential resistance mechanism. A thorough theoretical analysis of these single barrier NDR structures is presented.

The first experimental demonstration of the single barrier NDR mechanism is reported in chapter 3. The HgCdTe/CdTe material system was selected for the demonstration. In this material system, low temperatures (<20 K) are needed to observe the NDR effect. However, it has been demonstrated recently that room temperature NDR can be obtained from InAs/GaAlSb single barrier structures. High temperature (190-300 K) current-voltage curves from the single barrier Hg_1-xCd_xTe heterostructures have also been investigated, leading to a direct electrical measurement of the controversial HgTe/CdTe valence band offset.

In chapter 4, results are presented from several studies of III-V heterostructures grown by MBE. A measurement of the GaAs/AlAs valence band offset by xray photoemission spectroscopy yields a value of 0.46 ± 0.07 eV, independent of growth sequence. Optical measurements of electron tunneling times in GaAs/AlAs double barrier heterostructures are performed by growing structures with very thin cap layers. Tunneling times as short as ≈ 12 ps are measured. Triple barrier GaAs/AlAs tunnel structures are found to display strong NDR, indicating that the tunneling process is coherent (as opposed to sequential) in nature. Finally, a technique for depositing high quality InAs buffer layers on GaAs substrates is developed.

Thesis Files