Determination of surface barrier height and surface state density in GaN films grown on sapphire substrates
- PDF / 117,892 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 60 Downloads / 212 Views
E3.2.1
Determination of surface barrier height and surface state density in GaN films grown on sapphire substrates Seong-Eun Park1, Joseph J. Kopanski1, Youn-Seon Kang2, Lawrence H. Robins2, and Hyun-Keel Shin3 1 Semiconductor Electronics Division, National Institute of Standards and Technology Gaithersburg, MD 20899-8120 2 Ceramics Division, National Institute of Standards and Technology Gaithersburg, MD 20899-8520 3 Gwangju Techno Park, LED/LD Packaging Service Center, 958-3 Daechon-dong, Buk-gu, Gwangju 500-706, South Korea
ABSTRACT Photoreflectance (PR) modulation spectroscopy was performed to investigate surface properties of GaN films grown on sapphire substrates. From the period of the Franz-Keldysh oscillations, the surface electric field across the GaN space charge region was found to be (197 ± 11) kV/cm, which corresponds to a surface state density of 1.0×1012 cm-2. A surface barrier height of 0.71 eV was determined by fitting the dependence of the PR intensities on pump beam power density. We suggest that a deep level is formed at 2.68 eV above the GaN valence band edge due to the large density of surface states.
INTRODUCTION The wide bandgap III–V compound semiconductor GaN has received much interest as a promising material for photonic and electronic devices due to its favorable properties under conditions of high-temperature, high-frequency, high-voltage, and high-switching speed [1-2]. Additionally, the wide bandgap of GaN-related alloys has led to the successful fabrication of short wavelength (blue and ultraviolet) light emitting diodes and laser diodes. In order to fabricate high performance GaN-based device structures, it is essential to grow undoped GaN layers having high quality. In particular, the surface electronic properties such as surface barrier height and surface state density are critical in determining device gain and efficiency. The surface barrier height and surface state density have been investigated by capacitancevoltage [3], scanning tunneling spectroscopy [4], and photoreflectance (PR) spectroscopy [5] methods. Especially, PR measurements have been extensively used to investigate electronic properties of semiconductor surfaces due to its contactless and nondestructive nature. Various studies of optical and electronic properties in GaN have been performed by PR spectroscopy[67], however, few works on electronic properties of GaN have been achieved so far. In this work, the pump beam power density dependence of the PR spectrum was examined to determine the surface barrier height and the surface state density of GaN films. Furthermore, the energy level produced by surface states was also calculated.
E3.2.2
EXPERIMENT An undoped GaN layer with a thickness of 1.1 µm was grown on the c-plane of a sapphire substrate by metalorganic chemical vapor deposition. The background electron concentration was found to be 1.5×1017 cm-3 using Hall-effect measurements. PR spectra of the GaN layer were measured at room temperature with various pump power densities. Figure 1 shows the experiment
Data Loading...
