Abstract
Wide bandgap III-V compounds are the key materials for the fabrication of short-wavelength optical devices and have important applications in optical displays, optical storage devices and optical communication systems. Herein, the variable-angle spectroscopic ellipsometry (SE) measurements are performed to investigate the thickness and optical properties of beryllium-implanted gallium nitride thin films that have been deposited on (0001) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (LPMOCVD). The film layer details are described by using Parametric Semiconductor oscillators and Gaussian oscillators in the wavelength range of 200–1600 nm. The thickness, refractive indices and extinction coefficients of the Be-implanted films are determined at room temperature. Analysis of the absorption coefficient shows that the optical absorption edge of Be-implanted films changes from 3.328 eV to 3.083 eV in the temperature range of 300–850 K. With the variable temperature, Eg is demonstrated to follow the formula of Varshni. A dual-beam ultraviolet–visible spectrophotometer (UV–VIS) is used to study the crystal quality of samples, indicating that the quality of rapid thermal annealing (RTA) sample is better than that unannealed sample. By transport of ions in matter (TRIM) simulation and SE fitting the depths of Be implanted gallium nitride (GaN) films are estimated and in good agreement. The surface and cross-section morphologies are characterized by atomic force microscopy (AFM) and scanning electron microscope (SEM), respectively. The surface morphologies and thickness measurements of the samples show that RTA can improve crystal quality, while increasing the thickness of the surface roughness layer due to partial surface decomposition in the process of thermal annealing.
Highlights
Gallium nitride (GaN) based semiconductor materials have drawn intensive attention for a long time due to its some advantages of the large bandgap, high thermal conductivity and stable chemical properties
Sapphire substrates by using low-pressure metalorganic chemical vapor deposition (LPMOCVD) with trimethylgallium (TMGA) and ammonia (NH3 ) as the source precursors for Ga and N
In order to confirm the thickness of films, the cross-section micrographs are determined by scanning electron microscope (SEM)
Summary
Gallium nitride (GaN) based semiconductor materials have drawn intensive attention for a long time due to its some advantages of the large bandgap, high thermal conductivity and stable chemical properties It has been extensively used in high-temperature power devices, high-frequency microwave devices and light-emitting diodes [1,2,3,4]. A series of Be-implanted GaN thin films with different RTA processes were investigated by variable angle and temperature-dependent spectroscopic ellipsometry (SE). These optical properties were obtained in a spectral range of 200 to 1600 nm (6.2–0.77 eV). Transport of ions in matter (TRIM) simulation was carried out to verify the mean depth of Be ion implantation
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