Schottky barriers on n-type GaN films grown by low-pressure metalorganic chemical vapor deposition are characterized and derived. A thin Pt or a Pd layer is deposited by electron-gun evaporation to form Schottky contacts in a vacuum below 1×10−6 Torr. The Schottky barrier heights of Pt on the n-GaN film are determined to be 1.04 and 1.03 eV by current–voltage (C–V) and current density–temperature (J–T) measurements, respectively. Also based on C–V and J–T measurements, the measured barrier height of Pd on n-GaN is 0.94 and 0.91 eV, respectively. Schottky characteristics of Pt and Pd observed in the experiment are compared with those of Au and Ti in previous reports.

Se-doped GaN films are grown for the first time by low-pressure metalorganic chemical vapor deposition (LP-MOCVD), in which H2Se is used as the Se source gas. Effects of Se doping on electrical properties of GaN films are reported. Se atoms tend to out-diffuse to the surface of the GaN film at high temperature. The N atomic percentage is influenced by the incorporation of H2Se in the MOCVD process. The carrier concentration was found to be significantly affected by the surface defects which develop at high H2Se dosages. The highest free electron concentration obtained is about 1.5×1018 cm-3. Increasing the growth temperature from 1000° C to 1050° C reduces the maximum carrier concentration to about 7×1017 cm-3.

GaN films were successfully grown by the remote-plasma metalorganic chemical vapor deposition (RPMOCVD) system. The composition of the GaN films could be tuned from nitrogen-rich to stoichiometric growth by varying the mole flow rate of trimethylgallium (TMGa). A hypothesis concerning the collisions between excited nitrogen and TMGa was also brought up. The collision between excited nitrogen and TMGa influences the characteristics of surface morphology, composition, growth rate, and growth mechanism. The characteristics of the GaN film were optimized by changing the growth conditions. The narrowest FWHM of the double-crystal X-ray rocking curve is about 0.2°. Under optimized conditions, the composition of the GaN film is almost the same as that of the reference GaN film grown by MOCVD.

A quantum theory of noncommutative fields was recently proposed by Carmona, Cortez, Gamboa and Mendez ([1]). The implications of the noncommutativity of the fields, intended as the requirements [φ,, were analyzed on the basis of an analogy with previous results on the so-called "noncommutative harmonic oscillator construction". Some departures from Lorentz symmetry turned out to play a key role in the emerging framework. We first consider the same hamiltonian proposed in [1], and we show that the theory can be analyzed straightforwardly within the framework of Heisenberg evolution equation without any need of making reference to the "noncommutative harmonic oscillator construction". We then consider a rather general class of alternative hamiltonians, and we observe that violations of Lorentz invariance are inevitably encountered. These violations must therefore be viewed as intrinsically associated with the proposed type of noncommutativity of fields, rather than as a consequence of a specific choice of hamiltonian.

The influence of the growth procedure on the optical quality of InGaN grown on GaN has been investigated. The photoluminescence spectrum of the sample with a low-temperature-grown GaN cap layer or a graded-temperature-grown GaN cap layer has a shorter peak wavelength than that of the sample grown with a normal-temperature-grown GaN layer. The shift of the peak wavelength increases with the increase of the layer thickness for the sample with the low-temperature-grown GaN. This is because the defects contained in the low-temperature-grown GaN cap layer induce the outdiffusion of In atoms during the temperature-ramped procedure. The narrower linewidths and higher intensities of the PL spectra for InGaN after In outdiffusion may be due to the reduction of the strains, dislocations or defects. The Raman spectra and the Auger electron spectra also indicate that the low-temperature-grown GaN has a lot of defects which reduce the phonon peak intensity and induce the interdiffusion of In atom during the growth of GaN/InGaN heterostructures.

This work performs Si ion implantation the electrical conductive type of the p-GaN film from p-type to n-type. Multiple implantation method is also used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implant energies for the multiple implantation are 40, 100, and 200 KeV. The implant dose is 5×1015 cm-2 for each implant energy. After implantation, the samples are annealed in a N2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000°C. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implantation in p-GaN. Moreover, the rectifying I-V characteristic of the p-n GaN diode is also examined.

This work performs Si ion implantation to activate and convert the electrical conduction of p-GaN films from p-type to n-type. Multiple implantation method is used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implantation energies for the multiple implantation are 40, 100, and 200 keV. The implantation dose is 5 Â 10 15 cm 2 for each implantation energy. After implantation, the samples were annealed in an N 2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 o C,. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implant in p-GaN. In addition, the rectifying I±V characteristic of the p±n GaN diode is also examined.

Copper Schottky diodes on n-type GaN grown by metal-organic chemical vapor deposition were achieved and investigated. Ti/Al was used as the ohmic contact. The copper metal is deposited by the Sputter system. The barrier height was determined to be as high as (ΦB =1.13eV by current-voltage (I-V) method and corrected to be ΦB =1.35eV as considered the ideality factor, n, with the value of 1.2. By the capacitance-voltage (C-V) method, the barrier height is determined to be ΦB =1.41eV. Both results indicate that the sputtered copper metal is a high barrier height Schottky metal for n-type GaN.