| Summary: | 碩士 === 國立成功大學 === 電機工程學系 === 87 === GaN films were grown on the (0001) sapphire substrates by MOCVD using a horizontal reactor. The low-temperature GaN buffer layer, 250 A in thickness, was grown at 560℃. The high-temperature GaN films were grown at 1050℃. XRD observations indicated that the films are well oriented hexagonal GaN. But SEM observations showed that there were many micro-cracks and defects in the films. The films showed PL emission of λ≒358 nm. FWHM of the PL is 1nm.
Many important device, such as metal-semiconductor-metal (MSM)
Photodiode, metal-semiconductor field effect transistors (MESFETs), high electron mobility transistors (HEMTs) employ a Schottky barrier for at least one electrode. So a good and stable Schottky barrier is essential.
In this article we report experiment results of Schottky barrier contact on n-type GaN. The detail of the growth and crystal properties have been previously reported.[1,2]We using Au, Pd, Ni, Pt and Ti to as Schottky dot and Al was used for ohmic contact. Measurements were carried out by using current-voltage(I-V), current-voltage-temperature(I-V-T) and capacitance-voltage(C-V) techniques. The barrier, ideality factors and effective Richardson constant are presented. Contact of Ti exhibited only slight rectifying characteristics and small barrier. These result show that the barrier on n-type GaN increase with metal work function. This supports the prediction that Fermi level is not pinned at the GaN surface. Due to simple planar device structure that is compatible with FET and low parasitic capacitance, small area Metal-Semiconductor-Metal Photodiodes (MSM PDs) have been one of the most favored detector choices for high speed Optoelectronic Integrated Circuits (OEICs). The current interest in developing ultraviolet (UV) photodiodes is driven by applications in military counter measures, aerospace, automotive, petroleum, engine monitoring, flame detector and solar UV detection. The III-Nitride AlxGa1-xN wide direct band gaps are tunable from 365 nm (at x=0) to 200 nm (at x=1) and are direct over the entire alloy composition. These are ideal material for developing UV photodiodes due to the relatively high mobility, sharp cut-off wave length and high quantum efficiency. The technology of GaN UV detectors is still at a beginning stage of its development and although is now receiving intense investigation.
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