We report on the fabrication and characterization of solar blind photodetectors (SBPs) based on undoped β‐Ga2O3 and Zn doped (∼5 × 1020 cm−3) β‐Ga2O3 (ZnGaO) epitaxial films with cutoff wavelength of ∼260 nm. The epilayers were grown on c‐sapphire by the metal organic chemical vapor deposition technique and their structural, electrical and optical properties were characterized using various methods. As grown films have a large number of defects, resulting in detectors with enhanced internal gain, hence, high spectral responsivity >103 A/W. Post growth annealing in oxygen improved the quality of the epilayers, leading to detectors with reduced dark current (∼nA to ∼pA) and increased out of band rejection ratio. At 20 V bias, a ZnGaO detector showed a peak responsivity of 210 A/W (at 232 nm) and an out of band rejection ratio (i.e., R232 nm/R320 nm) of 5 × 104. Alternatively, for a β‐Ga2O3 detector these parameters were found to be five times and three times lower, respectively, suggesting that ZnGaO detectors have superior performance characteristics. These results provide a roadmap toward achieving high responsivity SBPs based on epitaxial ZnGaO films, laying a solid foundation for future applications.

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Metal-semiconductor-metal (MSM) structured solar blind photodetectors were fabricated based on various Mg content wurtzite Mg x Zn 1-x O epitaxial films grown via pulsed metal organic chemical vapor deposition. The response spectra of the devices showed a peak position that shifts from ~383 nm to 276 nm for Mg content, x, between 0.0 and 0.51, covering a wide portion of the ultraviolet spectral region, extending well into the solar blind window. At 10 V bias, a large responsivity of ~1.8x10 4 A/W was obtained at 276 nm for a device based on a high Mg content (x=0.51) MgZnO film. To the best of our knowledge, this responsivity is the highest ever reported for a MgZnO based device and its origin is attributed to large internal gain resulting from carrier trapping at the MgZnO/Ni/Au interface. This is confirmed by the presence of an asymmetric Schottky barrier height on the two MSM contacts. Conversely, the response speed of the devices was slow with the 10%-90% rise and fall times measured to be in the millisecond range. The results reported in this work show the realization of high responsivity MgZnO based solar blind photodetectors, providing a significant step in the development of MgZnO alloy based of detector.

The influence of RF power on the growth of N-polar AlN thin layers on Si(111) by plasma-assisted molecular beam epitaxy was systematically studied. The surface reconstruction of AlN was 1 × 1 for samples grown at RF power of 350–450 W, while samples grown at lower power of 150–300 W had 3 × 6 reconstruction. All samples demonstrate smooth surface with root mean square roughness less than 1 nm. The 45 nm thick AlN sample grown at RF power of 150 W has the best structural quality. The screw and edge dislocation densities estimated for this sample were 1.4 × 109 and 5.9 × 109 cm−2, respectively.

Crack‐free high quality N‐polar AlN epitaxial layers were grown on Si (111) substrates by plasma‐assisted molecular beam epitaxy in the temperature range of 780–880 °C. The streaky 1×3 reflection high energy electron diffraction pattern was observed at room temperature for all AlN samples indicating N‐polarity of epilayers. The polarity of samples was also confirmed by KOH etching studies. Structural properties of as‐grown samples were carried out by high resolution X‐ray diffraction, scanning electron microscopy, and atomic force microscopy. The Williamson‐Hall plots of the rocking curves widths were employed in order to study the mosaicity, dislocation density, and level of stress as a function of growth temperature. The 250 nm thick AlN sample grown at 830 °C yields the best crystalline quality, smooth surface morphology, and smallest root mean square roughness. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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