Patent issued for growth of cubic crystalline phase structure on silicon substrates and device compromising the cubic crystalline phase structure

October 31, 2019 - CHTM

The United States Patent Office issued Patent no. US 10,453,996 B2 on October 22, 2019 for "Growth of cubic crystalline phase structure on silicon substrates and device compromising the cubic crystalline phase structure" to University of New Mexico (UNM), Rensselaer Polytechnic Institute (RPI), and Current by GE.The UNM inventors are Dr. Steven R.J. Brueck and Seung-Change Lee. Brueck is a Distinguished Professor, Emeritus, Electrican and Computer Engineering; Physics and Astronomy; and Director Emeritus of CHTM. Seung-Chang Lee is a Research Associate Professor at CHTM. Other listed inventors are Christian Wetzel of Rensselaer Polytechnic Institute and Mark Durniak of Current by GE.

Abstract

 A method of forming a semiconductor structure includes providing a substrate comprising a first material portion and a single crystal silicon layer on the first material portion. The substrate further comprises a major front surgace, a major backside surface opposing ithe major front surface, and a plurality of grooves position in the major front surface. A buffer layer is deposited in one or more of hte plurality of grooves. A semiconductor material is epitaxially grown over the buffer layer and in the one or more plurality of grooves, the epitaxially grown semiconductor material comprising a hexagonal crystalline phase layer and a cubic crystalline phase structure disposed over the hexagonal cryrstalline phase.

Technical Field

The disclosure is directed to a method of growing cubic crystalline phase structure and devices made therefrom.

Background

 III-N semiconductors are promising optoelectronic materials whose direct bandgap optical emission spans the ultraviolet to infrared. Despite the impressive progress of visible light-emitting diodes (LEDs) in the nitride material system over the past two decades, two major issues are widely recognized: 1) the green gap, and 2) efficiency droop. The green gap refers to the fact that today's InGaN LEDs emitting in the green have lower efficiencies than comparable devices in the blue, or to red LEDs in the AlInGaP material system. This is an issue since the sensitivity of the human eye peaks in the green. Efficiency droop is the reduction in efficiency at high drive levels, suitable for illumination. The exact origins of these effects are not fully understood, but often the polarization fields in the InGaN wurtzite material system are thought to be a root cause.

GaN and alloys including AlGaN and InGaN (or GaInN) exhibit both hexagonal (wurtzite) and cubic (e.g., zinc-blende) phases. As used herein, the terms AlGaN, InGaN and GaInN are shorthand notations common in the field for Al.sub.xGa.sub.1-xN, In.sub.yGa.sub.1-yN and Ga.sub.1-yIn.sub.yN. For GaN and InGaN the hexagonal (h-GaN) phase is energetically preferred and with a few exceptions, all device applications including high-power transistors, light-emitting diodes (LEDs) and laser diodes have been developed with h-GaN material.

There are potential advantages to cubic (c-GaN) material and its alloys. One advantage is that the (001) direction (i.e., the direction of growth on the (001) crystal face) is not only free of spontaneous polarization, but also free of piezo-electric polarization. The bandgap of the cubic nitrides is slightly smaller than that of the wurtzite polytypes, and therefore the band-edge emission in bulk crystals of cubic GaInN has longer wavelength than in wurtzite crystals with the same indium concentration. The general absence of internal electric fields in c-GaN LEDs can eliminate the redshift associated with the quantum-confined Stark effect (QCSE).

Another potential benefit of cubic GaN is the high hole mobility, which is reported to reach 350 cm.sup.2V.sup.-1s.sup.-1 in cubic GaN on GaAs. A practical advantage of (001) c-GaN is that it can be cleaved along the {110} planes, which are perpendicular to the (100) growth direction. This could be a major advantage for device fabrication, e.g. the fabrication of laser diode devices. Further, based on theoretical calculations, it has been suggested that the Auger-recombination in the blue-green region could be smaller in c-GaInN structures than in their wurtzite counter-part. This could impact the efficiency droop effects.

According to the literature, c-GaN has been successfully grown by plasma assisted molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy (MOVPE) on different substrates, including 3C--SiC, 6H--SiC (as super lattice), GaAs, and Si (001). Also, growth of nano-wires with cubic GaN has been demonstrated by MBE. In the case of growth on GaAs, large free-standing samples with 100 .mu.m thickness have been achieved. Novikov et al., "Molecular beam epitaxy as a method for the growth of freestanding zinc-blende (cubic) GaN layers and substrates," J. Vac. Sci. Technol. B 28, vol. 28, no. 3, pp. C3B1-C3B6, October 2010. However, it took those authors around 8 days to grow such material. It remains difficult to keep optimal growth conditions for such long durations, and the best material quality was believed to have been achieved only within the first 10 .mu.m starting from the substrate. This thickness however would be sufficient for use in LEDs.

 

Source:

U.S. Patent No: 10,453,996

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