Observation of cyclotron resonance in CdSe below the metal-insulator transition

We report the observation of electron cyclotron resonance (CR) in n-type CdSe with an average carrier density below the metal-insulator transition ( N _d^{1}/{3}a ^∗ = 0.08 ). A plasma-shifted electron cyclotron resonance (SCR) is also observed. The number of carriers participating in cyclotron resonance, which is more than 4 orders less than N_d - N_a, increases rapidly with magnetic field, in agreement with a previous calculation based on Poisson distribution of donors. This supports the picture of metallic donor clusters within doped semiconductors due to random distribution of impurities. The simultaneous appearance of both CR and SCR is interpreted in terms of the breakdown of the Maxwell Garnett theory for random-donor semiconductors.