Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

Abstract

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β-Ga 2 O 3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

Identification and modulation of electronic band structures of single-phase β-(AlxGa1−x)2O3 alloys grown by laser molecular beam epitaxy

“…Meanwhile, the calculated electron effective mass values for (Al x Ga 1Àx ) 2 O 3 were found to increase by adding Al-ranging from 0.265 m e for x ¼ 0, to 0.376 m e for x ¼ 0.5 and finally to 0.437 m e for x ¼ 1. For b-Ga 2 O 3 , similar values were reported, both theoretically 13,32 and experimentally (0.28 m e ). 33 Recently, the effective mass of the 2DEG formed at (Al x Ga 1Àx ) 2 O 3 /Ga 2 O 3 (x ¼ 0.2) interface is estimated to be 0.313 m e , 7 which is related to the strong electron-electron interaction.…”

A novel β‐Ga2O3 HEMT with fT of 166 GHz and X‐band POUT of 2.91 W/mm

“…The β ‐Ga 2 O 3 material parameters such as total conduction band ( N C ) and valence band ( N V ) density of states of 3.6 × 10 18 cm −3 and 2.86 × 10 20 cm −3 respectively are calculated from electron and hole effective masses given in Reference 42, while other parameters are taken from Reference 17. Also acceptor and donor traps positioned at E C − E tA = 0.82 eV, E tD − E V = 4.4 eV 43 with density of 10 17 cm −3 are doped in β ‐Ga 2 O 3 layer.…”

Enhancing the intrinsic p-type conductivity of the ultra-wide bandgap Ga2O3 semiconductor

“…If VO •• defect is located in the first coordination spheres, its proximity can reduce electronic level of VGa' (1.24eV) by  1 eV, which is in a good agreement with Ea2 = 0.17eV activation energy observed in experiment. X-ray photoelectron spectroscopy (XPS) is a fine chemical method to investigate a material's valence band characteristic and brings additional evidence of the presence of states within the bandgap 57-59 57 When used in high resolution in the valence band vicinity (i.e., for the lowest binding energies), it is possible to directly detect whether there are states in the lower part of the bandgap (those responsible of the p-type character) 60 As shown in Fig. 4, it was found a clear correlation within the amount of states in the lower half of the bandgap and the p-type character in the sequence, n-type (Sidoped) commercial reference, p-type (undoped) and ptype (annealed).…”