Rhombohedral cubic semiconductor materials on trigonal substrate with single crystal properties and devices based on such materials

Inventors

Park, Yeonjoon • Choi, Sang Hyouk • King, Glen C. • Elliott, James R.

Assignees

National Aeronautics and Space Administration NASA

Abstract

Growth conditions are developed, based on a temperature-dependent alignment model, to enable formation of cubic group IV, group II-V and group II-VI crystals in the [111] orientation on the basal (0001) plane of trigonal crystal substrates, controlled such that the volume percentage of primary twin crystal is reduced from about 40% to about 0.3%, compared to the majority single crystal. The control of stacking faults in this and other embodiments can yield single crystalline semiconductors based on these materials that are substantially without defects, or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. These methods can selectively yield a cubic-on-trigonal epitaxial semiconductor material in which the cubic layer is substantially either directly aligned, or 60 degrees-rotated from, the underlying trigonal material.

Core Innovation

The invention develops methods and growth conditions for creating cubic group IV, III-V, and II-VI semiconductor materials in the [111] orientation on the basal (0001) plane of trigonal crystal substrates, specifically controlling stacking faults and twin crystals. This is achieved using a temperature-dependent alignment model that reduces the volume percentage of primary twin crystals significantly, from about 40% to about 0.3%, resulting in majority single crystal structure. The invention further allows selective formation of cubic-on-trigonal epitaxial semiconductor material with cubic layers either directly aligned or 60 degrees rotated from the underlying trigonal substrate.

The problem addressed is the difficulty and conventional belief of impossibility in growing single crystalline cubic semiconductor layers such as SiGe and other group IV, III-V, and II-VI materials in the [111] orientation directly on trigonal substrates like c-plane sapphire due to the formation of stacking faults and 60° rotated twin defects. Prior methods yielded high twin defect concentrations and poly-type crystalline structures, which limited device fabrication and material quality, especially for microelectronic devices requiring high crystal quality and for thermoelectric materials needing controlled phonon scattering.

The invention provides not only methods to reduce twin crystal volume and control stacking faults but also utilizes a temperature-dependent energetic model to select growth conditions that enable either nearly single crystalline growth or controlled polycrystalline structures for different device applications. It further introduces advanced non-destructive inspection tools, such as specialized X-ray diffraction methods and Electron Back Scattered Diffraction, for macroscopic wafer characterization enabling precise control and verification of the crystal quality and orientation during growth.

Claims Coverage

The claims define semiconductor materials and devices featuring rhombohedrally aligned cubic crystalline structures on trigonal substrates, covering two main configurations of azimuthal alignment, specific compositions and doping, and resulting semiconductor devices.

The claims cover two distinct azimuthal alignments of rhombohedrally aligned cubic semiconductors on trigonal substrates, defined material compositions including doped SiGe alloys on c-plane sapphire, and semiconductor devices leveraging these materials for advanced microelectronic applications.

Stated Advantages

Documented Applications