Xuemei Hua

Characteristics of GaN thin films by inductively coupled plasma etching with Cl2/BCl3 and Cl2/Ar

GaN thin films were etched by inductively coupled plasma (ICP). The effects of BCl3 and Ar with different Cl2 fraction are studied and compared. The ICP power and RF power are also altered to investigate the different effects by using Cl2/BCl3 or Cl2/Ar as etching gases. The etch rate and surface morphology of the etched surface are characterized by using surface profiler, scanning electron microscopy and atomic force microscopy. The root-mean-square roughness values are systematically compared. It is found that the etch rates of Cl2/Ar are higher than that of the Cl2/BCl3 in the Cl2 fraction ranging from 10 to 90%. When the ICP power is increased, the RMS roughness of GaN surface after ICP etching shows reverse trend between Cl2/BCl3 and Cl2/Ar gas mixture. The results indicate quite different features using Cl2/BCl3 and Cl2/Ar for GaN ICP etcing under the same conditions.

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Two-inch Ga2O3 films with ( )-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga2O3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga2O3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 eV.

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GaN nanorods are fabricated using inductively coupled plasma etching with Ni nano-island masks. The poly [2-methoxy-5-(2-ethyl)hexoxy-1,4-phenylenevinylene] (MEH-PPV)/GaN-nanorod hybrid structure is fabricated by depositing the MEH-PPV film on the GaN nanorods by using the spin-coating process. In the hybrid structure, the spatial separation is minimized to achieve high-efficiency non-radiative resonant energy transfer. Optical properties of a novel device consisting of MEH-PPV/GaN-nanorod hybrid structure is studied by analyzing photoluminescence (PL) spectra. Compared with the pure GaN nanorods, the PL intensity of the band edge emission of GaN in the MEH-PPV/GaN-nanorods is enhanced as much as three times, and the intensity of the yellow band is suppressed slightly. The obtained results are analyzed by energy transfer between the GaN nanorods and the MEH-PPV. An energy transfer model is proposed to explain the phenomenon.

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The frequency dependence of capacitance-voltage (C-V) characteristics of Hg/GaN and Hg/InGaN/GaN Schottky contacts are investigated for 1KHz, 10KHz and 1MHz at room temperature. An anomalous peak in the C-V curves of Hg/GaN sample is observed but no peak for the Hg/InGaN/GaN sample occurs. The interface states, series resistance and minority-carrier injection would be the origin of this anomalous peak. The interface states density is calculated through C-V measurement of high and low frequencies, and a four-element circuit model is proposed to determine the series resistance. In addition, energy bind structures are taken into account. The three aspects above are analyzed for both two samples, and the origin of the anomalous peak is attributed to the series resistance and minority-carrier injection rather than the interface states.

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In this work, the composition distribution in SiC films grown on Si(111) using chemical vapor deposition (CVD) method has been measured by the plan-view energy dispersive spectroscopy (EDS). The measuring original EDS data are modified by considering the multilayer structure and the attenuation due to the diffuse reflection at the interface of the voids. The relative error rate of the improved EDS data is reduced by ∼ 45% comparing to the measurement result of X-ray photoelectron spectroscopy. Such a modification shows that the plan-view EDS method can be an effective way for characterizing element content of the SiC/Si structure in semi-quantitative measurement.