Modifications of Defects Concentrations Induced by Ammonia Flow Rate and its Effects on Gallium Nitride Grown by MOCVD
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1195-B03-05
MODIFICATIONS OF DEFECTS CONCENTRATIONS INDUCED BY AMMONIA FLOW RATE AND ITS EFFECTS ON GALLIUM NITRIDE GROWN BY MOCVD. ,1 1 S. Suresh* , V. Ganesh , T.Prem Kumar1, M. Balaji1, V. Ganesan2, K. Baskar1 1 Crystal Growth Centre, Anna University, Chennai – 600 025, T.N, India 2 UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore (MP) 452001, India. Abstract Optical and schottky diode characteristics of unintentionally doped GaN films grown by MOCVD were reported. GaN epilayers were grown with different V/III ratio by varying the source ammonia (NH3) flowrate. It exhibit changes in the density of threading dislocations (TDs) and reduced carbon and oxygen impurity incorporation. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that on decreasing the ammonia flowrate, threading dislocations decreases. Low energy positron beam was employed to study the Ga vacancies in the epilayers. S-parameter vs. positron beam energy curves clearly shows increase in SL on increasing the V/III ratio indicating that the point defects trapping positron increases. Corroborative HRXRD, Photoluminescence and Hall measurements confirm the reduction in trapping defects and threading edge dislocations with reducing V/III molar ratio. The effects of such variation of compensating centres and radiative centres as a function of MOCVD growth conditions on optical properties and schottky device characteristics like radiative decay lifetime, barrier height and reverse leakage current respectively were discussed. Introduction Gallium nitride (GaN) is an attractive wide bandgap semiconductor which is known for its excellent light emitting properties in spite of having a high density of dislocations. The major problem in this material and its alloys is the presence of a large number of defects [1]. The extended defects deteriorate the optical and transport properties of epitaxial GaN. In spite of great importance to GaN, identification of defects and the understanding of crucial role of point defects in the properties of this materials and devices are still lagging [2]. Further insight into the growth parameter optimization, its effects on defects and its properties will allow us to develop high efficiency GaN based devices on different substrates also. Even though many electronic devices have been fabricated on the GaN and related alloy systems, degradation of electrical characteristics of the Schottky devices due to the variation in the density of compensating centers and threading dislocations have not been studied in detail and still in dispute [3], where much deeper understanding of compensation mechanism in GaN and interface properties are needed for developing reliable modeling of devices. Studies establishing correlation of device properties with the presence of type of non uniformities are absolutely necessary. And so are the studies of the growth factors suppressing or enhancing these non uniformities. In the present investigation, ammonia flow rate-
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