The Effect of Indium Surfactant on the Optoelectronic and Structural Properties of MBE Grown Gallium Nitride
- PDF / 399,737 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 34 Downloads / 189 Views
Mat. Res. Soc. Symp. Proc. Vol. 618 @2000 Materials Research Society
suggested that the surfactant lowers the energy barrier for the horizontal motion of Ga atoms. However, the lowering of surface energy by adopting As surfactant in wurtzite GaN is expected to be small[4]. The use of In as a surfactant in place of As has been investigated by Widmann et al.[4] Initial results indicated that the technique improves two-dimensional (2-D) growth of GaN. In this paper, we report a systematic study on the effects of indium surfactant on the optical and structural properties of undoped GaN epilayer grown by plasma assisted MBE. The films were examined by photoluminescence (PL) spectroscopy, high resolution x-ray diffraction (HRXRD) and atomic force microscopy (AFM). Further investigation in the film quality was done by low-frequency noise measurement which is a powerful characterization tool for the nature of defects in semiconductor materials. The results are used to provide a basis for further elucidation of the effects of indium surfactant on the optical and structural properties of GaN films. Experiment The undoped GaN epilayers were grown on (0001) sapphire substrates by MBE. The sapphire substrates were first outgassed at 850'C for 30 minutes in ultra-high vacuum for thermal cleaning. The temperature was then lowered to 550'C and substrates were exposed to plasma activated nitrogen for the nitridation of the substrate surface. Subsequently, approximately 200 A of a low-temperature GaN buffer layer was deposited. The substrate temperature was raised to 770'C for the growth of the epilayer. High purity metallic Ga and In were evaporated by EPI SUMO cells and N2 gas was excited by EPI UNI-Bulb nitrogen plasma source. The In flux was kept at about 1/10 that. of the Ga flux. Sample A was grown with a small In flux while sample B was grown in exactly the same experimental condition except that no In surfactant was used in this case. Room temperature PL measurements were done using a HeCd laser as the excitation source. The luminescence was dispersed in a 1/8 m spectrometer and detected by a photomultiplier tube. Atomic force microscopy observations were made in air at room temperature using a Digital Instruments Nanoscope III. Large field 125 Am x 125 Am peizo heads were used with standard Si3 N4 cantilevers. The images were acquired using constant force mode with the force set at 10 nN. The HRXRD experiment was carried out with Cu Killine radiation (1.54056 A), monochromated by a four-crystal Bartels monochromator. To examine the low-frequency noise of GaN thin films, cross-bridge resistive structures were fabricated by reactive ion etching. Ti/Al bilayer ohmic contacts were formed by sputter deposition. The contact resistance was characterized by a linear configuration of rectangular pads utilizing the transmission line model. Low-frequency noise was studied over a wide range of temperatures from room tempeature to 90K over the frequency range of 80 Hz to 100 kHz. Detailed description of the low-frequency noise experim
Data Loading...
