Abstract
The authors report that the growth rate of ZnO can be significantly increased by modifying the oxygen plasma conditions in plasma-assisted molecular beam epitaxy. Both the aperture diameter and the distance between the plasma source and the substrate affect the growth rate and the quality of the ZnO films. A short source to substrate distance is essential in achieving higher growth rate, which is explained by reduced chance of oxygen atom collisions to accommodate the short oxygen mean free path at high background pressure. At a shorter source to substrate distance, the growth rate is higher with a larger aperture diameter. The quality of the ZnO thin films grown under different conditions is assessed by x-ray diffraction and room-temperature photoluminescence measurements.
Highlights
ZnO is a wide bandgap semiconductor with a direct bandgap of 3.37 eV at room temperature
Sample A was grown with a long source to substrate distance (42 cm) while samples B and C were grown with a short source to substrate distance (25.5 cm)
We have studied the growth of ZnO thin films under different plasma configurations and found that the growth rate can be increased by reducing the distance between the radio frequency (RF) source and the substrate
Summary
ZnO is a wide bandgap semiconductor with a direct bandgap of 3.37 eV at room temperature. More efficient light emitting devices may be realized due to the large exciton binding energy of ZnO (60 meV) [1,2]. ZnO is a potential candidate for intersubband devices [3], especially for terahertz quantum cascade lasers working at room temperature [4], which is benefited from its large optical phonon energy (72 meV) [5]. Critical parameters for PAMBE growth of ZnO are Zn flux, O2 flow, substrate temperature, and plasma power [8]. It has been reported that the growth rate of ZnO increases with the increase of plasma power [9,10]. We report that the distance between the RF source and the substrate as well as the aperture diameter significantly affects the growth of ZnO thin films
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