Characterization of High Quality Continuous GaN Films Grown on Si-Doped Cracked GaN Template
- PDF / 1,000,360 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 70 Downloads / 228 Views
C3.34.1
Characterization of high quality continuous GaN films grown on Si-doped cracked GaN template C. B. Soha, J. Zhanga, D. Z. Chib,* and S. J. Chuaa,b# a) Centre of Optoelectronics, Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 b) Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 ABSTRACT In this paper, deep level defects in high quality continuous GaN films grown over a cracked Si-doped GaN template has been studied using digital deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). From TEM observation, it is found that the density of pure screw dislocations have been effectively suppressed while pure edge dislocations remained in substantial quantity. From DLTS measurement, trap levels at Ec -ET ~ 0.11-0.12 eV, 0.24-0.27 eV, 0.60-0.63 eV were detected in the high quality GaN layer. DLTS measurement was also carried out on the underlying cracked Si-doped GaN template after the top high quality continuous GaN film was removed by plasma etching. An additional defect level at Ec-Et ~ 0.37 eV was detected which we attributed to defect decoration at screw dislocation. Both the trap levels Ec-ET ~ 0.24–0.27 eV, 0.60-0.63 eV are believed to originate from mixed screw/edge dislocation based on observation of the logarithmic capture behavior. Trap level at Ec -ET ~ 0.24-0.27eV, however, experiences a more drastic increase in transient capacitance (i.e. in trap concentration) compared to that of Ec -ET ~ 0.60-0.63 eV after plasma etching, illustrating that the latter is related to a higher proportion of edge dislocation. The 0.11-0.12 eV trap level, which exhibits an exponential capture kinetic, is believed to be related to nitrogen vacancies. This high quality continuous GaN layer can be used as a template to grow any device structure and the underneath cracked Si-doped GaN layer may help to release stress for the top continuous GaN layer. This can bring about a cracked free epilayer for subsequent device fabrication. INTRODUCTION The wide bandgap semiconductor GaN shows great promise for blue light emitting diodes and ultraviolet laser diodes [1,2] as well as high power and high temperature electronic devices [3,4]. In the search of materials with high luminescence efficiency, GaN and its related materials have edged its competitors for instance ZnSe and SiC to be used as the active layer in blue –light emission optoelectronic devices. In order to produce a material of high quality and yield, the GaN epitaxial layer on which the devices are to be fabricated must have a low defect density. The ability to produce this high quality crystalline layer is greatly determined by the substrate on which the epitaxial layer is grown [5]. 6H-SiC [6] has the lowest lattice mismatch (3.5%) with GaN but its high cost makes it commercially unviable. Sapphire is the most commonly used substrate with larger mismatch of 13% give rise to a high density of threading dislocation (TDs) approximately 1×108 - 1×1012 cm-2. T
Data Loading...
