Free electron screening mechanism of the shallow impurity breakdown in n-GaAs: evidences from the photoelectric Zeeman and cyclotron resonance spectroscopies

Abstract

A novel breakdown (BD) mechanism of shallow impurity under the electric field at low temperatures is suggested for n-GaAs samples with the donor concentrations $N_D=10^{14} \div 10^{16}cm^{-3}$ and the compensation degree $K=\frac{N_A}{N_D}=0.3 \div 0.8$ with acceptors of concentration N_A in the external magnetic fields up to H=6.5~T. Diagnosis of the BD mechanism was performed by SI Zeeman and cyclotron resonance photoelectric spectroscopy methods in the wide interval of the electric field including the BD region too. The obtained results reveal that the BD electric field $\mathcal{E}_{BD}$ does not correlate with $K$ and the carriers mobility $\mu$ of the samples, which contradict to the well-known impact ionization mechanism (IIM). A serious discrepancy with IIM is that, $\mathcal{E}_{BD}$ does not almost depend on the magnetic field up to H=6.5~T when $\mathcal{E}\| H$, though the SI ionization energy increases two times. The cyclotron resonance (CR) measurements show that the line width does not depend on the electric field for $\mathcal{E}<\mathcal{E}_{BD}$ indicating the lack of free carriers (FC) heating in contradiction with IIM. A considerable decrease of the free carriers' capture cross section (CCS) by ionized SI centers with a subsequent increase in the FC concentration n is observed by means of PES investigation of the $1s \to 2p_{+1}$ and CR lines in the electric fields $\mathcal{E} \leq \mathcal{E}_{BD}$ and at different magnetic fields, applied along $H\| \mathcal{E}$ or perpendicular $H\perp \mathcal{E}$ to the electric field. Various effects determined in the PES measurements at $\mathcal{E} = \mathcal{E}_{BD}$, such as a drastic narrowing the $1s \to 2p_{+1}$ and CR lines, a shift of the CR line to higher magnetic fields and disappearing of the lines to higher excited SI states, were clarified to be a result of screening of SI Coulomb potential by free carriers.