The investigation of structural defects and surface states on GaN films
|關鍵字:||氮化鎵;缺陷;表面態;蕭基二極體;吸收光譜;GaN;defect;surface state;Schottky diode;XAFS|
Electrical and optical measurements, including Hall, current-voltage, photocapacitance, capacitance-voltage, deep level transient spectroscopy and x-ray absorption measurements, etc, has been employed to investigate the following effects, respectively. First, the various effects of structural defects and surface states on GaN films through the incorporation of In, As and Mg atoms into GaN with or without post-annealing have been intensively studied. Secondly, the novel observation and the detailed discussion of the long-term photocapacitance decay behavior will be reported. And at last, the influence of various surface treatments on surface states and the passivation of GaN surface will be taken up. Some salient features in our findings are listed as follows. (1) A trap-center related to arsenic is found located at 0.769 eV below the conduction band, which behaves most likely antisite in nature. (2) A decay phenomenon with logarithmic feature is found in the photocapacitance measurements and is relevant to the effect of traps associated with dislocations. By the way a technique is developed to retrieve the logarithmic time constants and capture cross sections as well. Moreover, (3) the effects of thermal annealing on Mg-doped GaN films are found to be anisotropic with respect to the crystal axes and have the greatest crystal microstructural change along the perpendicular of the epifilm surface. The effects also involved shifting of the structural mixing ratio between polytypes and increasing of Debye temperature of the films. In addition, we develop a method to characterize the surface states on p-GaN surface, and we use this method to analyze the p-GaN Schottky diodes with various surface treatments. As a whole, some important remarks on the practical viewpoints for operation and design of the possible modern electronic devices are worthy noted. On the isoelectronic In doping, we found In isodoping can effectively suppress the formation of deep levels and improve the electrical properties of n-GaN Schottky diodes, indicating that the isoelectronic In doping technique is a viable way to improve the n-GaN film quality. This has been confirmed by the results of photocapacitance measurements. As for the thermal annealing effects, we found the electrical properties of As-implanted GaN films can be recovered to that of the un-implanted ones, and all the findings on the Mg-doped GaN films indicated crystal structure relaxation towards a more stable hexagonal wurtzite configuration and atomic rearrangement to a more orderly condition after annealing. Finally on the surface treatment effects of p-GaN Schottky diodes, we realized the p-GaN Schottky diode with the ideality factor down to the value of 1.14 through the sulfide pretreatment, maybe nearly ideal optimization on the operation of p-GaN Schottky diodes currently.
|Appears in Collections:||Thesis|
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