Partially polycrystalline GaN1-xAsx alloys grown on GaAs in the middle composition range achieving a smaller band gap
Journal
Japanese Journal of Applied Physics
Journal Volume
56
Journal Issue
8
Date Issued
2017
Author(s)
Abstract
GaN1-xAsx alloys have been successfully grown on (100) GaAs substrates over a wide composition range (0.15 x 0.98) by plasma-assisted molecular beam epitaxy. In the middle composition range, the weak and broad (111) diffraction peaks are observed in the X-ray diffraction patterns. These diffraction peaks most likely come from small crystalline grains within the amorphous matrix and are unlike the entirely amorphous GaNAs alloys grown on sapphire and Pyrex glass. A transmission electron microscopy micrograph of the GaN0.50As0.50 alloy also shows a weak periodic structure consisting of small polycrystalline grains. To study the band gap and the As-affected spin-orbit band to conduction-band minimum transition, photomodulated reflectance is utilized. The band gap energies range from 0.78 to 2.15 eV (3.4 eV for end-point compounds GaN). Finally, the original and modified band anticrossing (BAC) models for GaNAs alloys were thoroughly verified over the entire composition range. Remarkably, the band gap energies of the partially polycrystalline GaNAs alloys agree well with those obtained using the original BAC model in the middle composition range because the model has been developed for crystalline materials. These results improve the growth of highly mismatched GaNAs alloys with different substrates and should expedite studies of high-efficiency multijunction solar cells fabricated using such a single ternary alloy system. © 2017 The Japan Society of Applied Physics.
Other Subjects
Amorphous alloys; Amorphous materials; Crystalline materials; Energy gap; Gallium arsenide; High resolution transmission electron microscopy; Molecular beam epitaxy; Polycrystalline materials; Sapphire; Semiconducting gallium; Ternary alloys; Transmission electron microscopy; X ray diffraction; Amorphous matrices; Band anti-crossing models; Conduction-band minimum; Different substrates; Photomodulated reflectance; Plasma assisted molecular beam epitaxy; Polycrystalline grains; Ternary alloy systems; Gallium alloys
Type
journal article