The electric sub-band structure of electron accumulation layers in InSe from Shubnikov-de Haas oscillations and inter-sub-band resonance

Abstract

In bulk InSe crystals grown by the Bridgman method, electron accumulation layers are formed in the vicinity of stacking faults with charged impurities adsorbed to the defect plane. Shubnikov-de Haas experiments show that the 2D electron gas in InSe observed at low temperatures has a density of 1012 cm-2 and that several dielectric sub-bands are occupied. The g-factor is enhanced by electron-electron interactions. The optical absorption was studied in the frequency range 3-20 meV in perpendicular and tilted magnetic fields up to 8T. The cyclotron resonance at Eres=h(cross) omega c, the intersubband resonance at Eres=E01 and the combined resonance at Eres=E01+h(cross) omega c, are all observed for both parallel and tilted polarisation, where E01 is equal to the sub-band separation as deducted from the Shubnikov-de Haas periodicities. With increasing magnetic fields the exciton-and depolarisation-shifted resonance E01 approaches the true sub-band splitting E01, and is the same time reduced in amplitude. Absorption due to bulk 1s-2p transitions in isolated shallow donors is also observed. The 2p level shows a three-dimensional Zeeman splitting (h(cross) omega c)3D with a weak anomalous mass anisotropy as observed in cyclotron resonance measurements of bulk carriers at temperatures of 30-100K. The effective electronic Rydberg is in agreement with results of exciton spectra.