Electrical characterization of process and irradiation induced defects in GaAs

Abstract

Gallium arsenide (GaAs) technology leads the implementation of high frequency devices with superior performance. A vast number of optoelectronic applications are based on the material owing to its direct and wide bandgap. Over the years the number of these applications continues to grow but they remain highly cost-ineffective partly due to the growth techniques and the presence of defects in GaAs. These areas have been researched on intensively over the past four decades with much controversy, particularly on the subject of the EL2 defect. This defect plays an important role in the design and operation of GaAs based devices. It is therefore important to understand its electronic properties and influence on device operation. Schottky barrier diodes (SBDs) were fabricated on n-type GaAs. The quality of the contacts was evaluated using current-voltage (I-V) and capacitance-voltage (C-V) measurements before and after exposing them to different processing techniques and radiation types. Deep-level transient spectroscopy (DLTS) and Laplace deeplevel transient spectroscopy (L-DLTS) were used to characterize the electrically active defects in the material. Defects with almost similar emission rates which were not observed in the past were identified using L-DLTS due to its high resolution. I-V and C-V measurements on as-deposited Au/n-GaAs SBDs in the 80 ?? 480 K range showed that the EL2 defect has a profound effect on the diode characteristics. The influence of the defect caused the temperature dependent behavior of the C-V barrier height to be split into two temperature intervals, each with a unique temperature coefficient. Exposure of the devices to temperatures above 300 K resulted in the deterioration of their I-V characteristics. Permanent physical modification of the SBDs was observed at 400 K and above. Inductively coupled plasma (ICP) etching, Electron beam deposition (EBD) and electron beam exposure (EBE) were observed to impact significantly on diode I-V and C-V characteristics. ICP etching resulted in devices with a lower reverse leakage current and high barrier height whereas EBD fabricated devices exhibited the poorest characteristics. DLTS results revealed that processing introduced electrically active defects in the bandgap. EBE induced defects had different electronic properties to all the processing and radiation induced defects observed in previous studies. I-V and C-V characteristics of SBDs exposed to alpha and beta-particle irradiation were identical to as-deposited samples. This demonstrated the radiation hardness of GaAs. DLTS spectra of alpha-particle irradiated SBDs displayed the defect peaks sitting on a skewed baseline which hampered accurate L-DLTS measurements. In addition to the prominent irradiation induced defects, high energy electron-irradiation was observed to induce defects with electronic properties similar to those of the EL2.