SBIR-STTR Award

Based on a combination of physical, electronic and optical properties, a semiconductor materials system (aluminum, gallium, indium nitride) has emerged over the last two years as the clear choice for fabricating optical devices producing green, blue, and ultra-violet light. These materials are very attractive for use with advanced sensors for use in detecting and monitoring, for instance, the illegal diversion of nuclear weapons materials. However the widespread use of nitride-based devices is currently limited by fabrication yield due to the lack of a suitable starting substrate material. The choice of the starting substrate is crucial for insuring the quality of subsequent device layers. In this project a new wafer substrate for the nitride-based Light-Emitting Devices (LEDs) will be used to eliminate a major source of device defects (and consequently yield loss). This substrate consists of a low defect density gallium nitride prepared by hydride vapor phase epitaxy. In Phase I the material synthesis technology of key elements of LEDs will be developed on the gallium nitride substrates. A functional device having blue light emission will be demonstrated at the end of Phase I. The demonstration of high brightness blue and green LEDs will be the goal of Phase II.

Commercial Applications and Other Benefits as described by the awardee:
High brightness blue and green LEDs are essential components in the design of full-color displays, high density data storage systems, and spectroscopic analysis systems. The LEDs are also potential candidates for replacing incandescent lamps (e.g., traffic signals) because of their low power consumption and long life. The gallium nitride substrate proposed for use in this program could potentially become the substrate of choice for all nitride-based devices. Finally the device technology developed in Phase I and Phase II would be directly applicable to the fabrication of blue semiconductor lasers.

Short wavelength (350-420nm, UV/blue) semiconductor light-emitting diodes (LEDs) and laser diodes will revolutionize the design of high density optical storage systems as well as optical and UV sensors. The DOE would have a need for such sensors to detect and monitor the illegal diversion of nuclear weapons material. Based on a combination of physical, electronic, and mechanical properties, III-V nitrides have emerged over the last two years as the material system of choice. However, proliferation of III-V nitride-based LEDs is limited by fabrication yield. This project will eliminate a major source of device defects (and consequently yield loss) by demonstrating III-V nitride LEDs on a new substrate: a low defect density GaN substrate prepared by hydride vapor phase epitaxy (HVPE). Phase I demonstrated the growth of high quality GaN and InGaN films on the HVPE GaN-on-sapphire substrates. InGaN/GaN double-heterostructure LEDs with low turn-on voltages and good electroluminescence were achieved. LEDs were fabricated with emissions covering the range between 420 to 540 nm. Finally, optically pumped lasing was achieved in InGaN/GaN heterostructures, demonstrating the high quality of the InGaN films as well as the smoothness of the interfaces in the heterostructure. Phase II will develop high brightness/narrow spectrum GaN-based LEDs with peak wavelengths from 365 nm to 420 nm for use in spectroscopy applications and will fabricate InGaN/AlGaN multiple-quantum-well (MQW) LEDs with narrow spectral widths on the order of 10 nm. These devices will have output powers of at least 1 mW and lifetimes >1000 hrs.

Commercial Applications and Other Benefits as described by the awardee:
High brightness ultraviolet, blue, and green light emitting diodes should have applications in optical data storage, full color displays, printing, traffic signals, general lighting applications, as well as spectroscopy applications. The high brightness and high efficiency should also reduce the energy consumption of these devices compared to those currently available.