Optical Properties of Wurtzite-and Zincblende-GaN Films Grown by RF Plasma-MBE
- PDF / 255,722 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 7 Downloads / 232 Views
F. SEMENDY*, N. BAMBHA*, J.G. KIM**, H. LIU**, AND R.M. PARK** * Army Research Laboratory, Fort Belvoir, VA 22060, [email protected] ** Department of Material Science and Engineering, University of Florida, FL 32611
ABSTRACT Both wurtzite-and zincblende-GaN films have been grown on sapphire and MgO substrates, respectively, and examined by photoluminescence and x-ray analysis. GaN films were grown on suitably prepared A12 0 3 and MgO substrates by molecular beam epitaxy employing a rf plasma discharge, nitrogen free radical source. The wurtzite-and zincblende-GaN films exhibited dominant near band-edge emission, the nature of which will be compared and contrasted for both phases in this paper. X-ray diffraction data for both phases will also be discussed.
INTRODUCTION GaN and related materials are considered to be excellent materials for applications of optoelectronic devices that operate in the near-UV as well as in the visible regions with appropriate bandgap modifications. GaN and its solid solutions such as AIGaN and InGaN have been used in the development of ultraviolet sensors,1 blue light emitting
diodes 2, photodetectors 3,and heterostructure field-effetc transistors 4 and optical pumping structures 5. In all cases wurtzitic materials are used for device structures. However, these hexagonal materials are difficult to cleave and hence lasing action in an appropriate structure may be difficult to obtain. Furthermore p-doping in the a-GaN is rather difficult. Zincblende GaN (0-GaN), which is thermodynamically metastable phase of GaN, is thought to be easier to cleave and p-dope. With the current success in making long lasting blue light emitting devices using GaN, its detailed optical behavior in both a and P phases should be studied under varying conditions. Significant knowledge is available on a-GaN, 6 7, whereas data on zincblende GaN particularly grown on MgO are scarce 8,9. Optical properties of cubic and hexagonal GaN in the regions of the fundamental gaps were studied by J. Petalas et al 1 who found that the gap of hexagonal GaN is larger than that of the cubic polytype.
547 Mat. Res. Soc. Symp. Proc. Vol. 395 ©1996 Materials Research Society
EXPERIMENTAL Film-growth experiments were carried out in a Varian Gen II MBE system with a base pressure of 1010 Torr range. The substrates used in this work were highly polished A12 0 3 (0001), and MgO (001) wafers of 1 cm. square. Both types of substrates were degreased in successive rinsing of trichloroethane, acetone, methanol, and isopropyl alcohol. The A1203 wafers were then etched in hot (160 0C) 3:1 H 2SO 4: H3PO 4. The samples were dried by blowing dry nitrogen and mounted on a strain-free MO holder, and then inserted into the vacuum system. The substrates were heated to - 730' C for 30 minutes. Sharp lines (lxl) were observed in the RHEED pattern. Growth temperature was between 650 0 C to 7000 C for both of these substrates. Fig.1 shows the MBE chamber with rf plasma source. N2
rf plasma discharge chamber
Electron Gun
(RHEED) Ion
Gauge
,,o
Data Loading...
