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.
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