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The characteristics of the spatial distribution of electron cyclotron resonance (ECR) plasma in an ECR-plasma enhanced metalorganic chemical vapour deposition system with a divergent magnetic field are investigated by a single Langmuir probe. The results show that the spatial distribution in the resonance room has a significant density gradient in both radial and axial directions. The ECR plasma density attains its highest value, about 3.0 × 10 11 cm −3 , at a position that moves away from the ECR point in the direction of the microwave window for about 2.5 cm. This peak is about ten times higher than the central plasma density in the downstream of the reactor chamber. Analysis of the spatial distribution in the reactor chamber shows that the ECR plasma in the upper region has poor radial and axial uniformity of plasma density and electron temperature under the influence of the magnetic field, whereas the plasma in the downstream region has fine radial uniformity. This excellent uniformity has extensive application in plasma processing. Furthermore, there is a maximum plasma density and a maximum electron temperature corresponding to a proper magnetic current. A change of magnetic current does not distort the characteristics of spatial distribution in the reactor chamber.

Capacitance-voltage (C-V) measurement is an effective method that has been widely used to study the electronic characteristics of the pn junction. In this paper, the C-V measurement is used to study the effect of the temperature on the structural type of the GaN-based pn junction. The C−2-V and C−3-V curves, combined with power-law index k, are used to determine the structural type of the GaN-based pn junction when the temperature is set at 25 °C, −50 °C, −100 °C, −150 °C, and −195 °C. Our experimental results show that the C−2-V curve is a clear linear relation, and the index k is 0.5 when the temperature is set at 25 °C and −50 °C. This shows an abrupt junction when the temperature ranges from 25 °C to −50 °C. When the temperature is dropped to −100 °C, the structural type of the pn junction begins to change and the index k becomes 0.45. When the temperature is decreased further to T = −150 °C and −195 °C, the index k becomes 0.30 and 0.28, respectively, corresponding to a non-abrupt and non-linear junction. Possible explanations of this phenomenon are: the low-temperature carrier freeze-out effect and the localized space charge region that is produced by crystal defects and interface states. The enhancement of the inhomogeneous and localized space charge region further affects the structural type of the pn junction in a low temperature environment.

In order to deposit good films, we need to study the uniformity of plasma density and the plasma density under different gas pressures and powers. The plasma density was diagnosed by a Langmuir probe. The optical emission spectroscopy (OES) of CH4 and H2 discharge was obtained with raster spectroscopy, with characteristic peaks of H and CH achieved. Diamond-like carbon films were achieved based on the study of plasma density and OES and characterized by atomic force microscope (AFM), X-ray diffraction instrument (XRD), Raman spectroscope and profiler.