GaN based quantum dot heterostructures
- PDF / 448,437 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 222 Views
GaN based quantum dot heterostructures M. A. Reshchikova, J. Cuia, F. Yuna, A. Baskia, M. I. Nathanb, and Hadis Morkoça a
) Virginia Commonwealth University, Richmond, VA 23284-3072,E mail: [email protected] ) On leave from University of Minnesota, Minneapolis, MN
b
ABSTRACT GaN dots have been grown on c-plane sapphire and (111) Si substrates by reactive molecular beam epitaxy. A new method involving two-dimensional growth followed by a controlled annealing during which dots are formed was employed. Due the dot nature and large dot density, relatively high luminescence efficiencies were obtained on both substrates. Single layer dots were used for AFM analysis whereas 30 layer dots were used for photoluminescence experiments. AlN barrier layers, some too thick for mechanical interaction, some thin enough for vertical coupling were used. Strong polarization effects lead to a sizeable red shift, which depends on the size of the dots. INTRODUCTION Gallium nitride and its alloys with InN and AlN have recently emerged as important semiconductor materials with applications to yellow, green, blue and ultraviolet portions of the spectrum as emitters and detectors, and as high power/temperature electronics.1-6 Nitride-based light emitting diodes (LEDs) with lifetimes approaching 100,000 hours (extrapolated) and brightness near 70 lm/W in the green have been obtained. These LEDs are already being used in full color displays, moving signs, traffic lights, instrumentation panels in automobiles and aircraft, airport runways, railway signals, flashlights, underwater lights. The technology is in the process of being extended to standard illumination under the name “ Solid State Lighting” (SSL). SSL is expected to result in substantial energy savings by as much as a factor of six compared to standard tungsten bulbs. Along similar lines, blue lasers are being explored as the read and write light source for increased data storage density for the next generation of digital video disks (DVDs). Already, the room temperature CW operation in excess of 10,000 hours has been reported. To be versatile, this level of lifetime with a power level of about 20 mW at 60 C is required. The present device lifetimes under these more stringent operating conditions are near 400 hours which is a long way from the needed 10,000 hours. The large bandgap of GaN with its large dielectric breakdown field, coupled with excellent transport properties of electrons and good thermal conductivity, are well suited for high power electronic devices.7 Already, high power modulation doped field effect transistors (MODFETs) 8 with a record power density of nearly 10 W/mm in small devices, and a total power of 8 W in large devices have been achieved9, with recent results of over 12 W. In addition to high power, and high frequency operation, applications include amplifiers that operate at high temperature and other unfriendly environments, and low cost compact amplifiers for earthbound and space applications.7
T4.5.1
When used as UV sensors in jet engines, automobiles
Data Loading...
