Plasma Shift of Cyclotron Resonance Line in n‐GaAs

Abstract

The detection of cyclotron absorption by change in static conductivity is a sensitive method for many semiconductors. The high sensitivity of this method allows to detect the cyclotron absorption at low temperatures T when the thermal energy kT is much smaller than the ionization energy of shallow impurities and the free electron concentration is too small.By applying shallow impurity break-down electric fields, the free electron concentration drastically increases and it causes some interesting physical effects concerning the CR line shape (linewidth and its position). The influence of free electrons on the CR line shape is different at high and low magnetic fields. At high magnetic fields l c % a i (lc magnetic length, < effective Bohr radius) we observed a positive shift (A B > 0) of the CR line in n-GaAs in break-down electric fields / l / . This effect was believed to be caused by the influence of free electrons screening on the value of the potential fluctuation.At low magnetic fields the influence of free electrons on the CR line shape is mainly due to the plasma shift towards &he low magnetic field direction which increases with decreasing magnetic field.In this letter we report the results of plasma shift investigations of the CR line in n-GaAs. CR measurements were carried out at liquid helium temperature using a laser magnetic spectrometer at fixed radiation wavelength A. = 337 p m of a continuous HCH laser. The change of static conductivity of the specimen under radiation was recorded a s a function of magnetic field.Epitaxial n-GaAs layers with ND = 1 0 to 1 0 cm , k = N /N = 0.35 to 0.65, p77 = (10 to 5.7)xlO cm V were used. The measurements were carried out in Voigt geometry with 3 1 H. The temperaturerise is estimated to be less than 0 . 1 K even for the strongest electric fields used in experiments.

Free-Electron Screening Mechanism of the Shallow Impurity Breakdown in n-GaAs: Evidences from the Photoelectric Zeeman and Cyclotron Resonance Spectroscopies

“…At the breakdown electric field, free electrons with the concentration n, determined by the current density j = enµ c E BD , are generated in the conduction band. Beside n free electrons, there appear the same amount of positively charged donors, and the charge concentration becomes N I = 2KN D + n. The free electron concentration n even at strong breakdown E = E BD amounts to a few percent of the total neutral donors n ≪ N I ≈ 2KN D , which was confirmed by the experimental studies of the plasma shift of the CR line in n − GaAs [28].…”

“…our sample 5 at λ = 119 µm. The shift fails at relatively small magnetic fields (H = 21 kOe), and its value increases with the magnetic field from H = 43 kOe to H = 61 kOe [28].…”

“…Nevertheless, at the electric fields, higher than the breakdown value E > E BD , and H ≈ 21 kOe a correction to the effective mass due to the plasma shift becomes essential [28]. A considerable shift in the CR line to the small magnetic field (Fig.…”

“…( 26), seems to be one order higher than that determining from Eqs. ( 27) and (28). One of the peculiarity of the CR measurements in n − GaAs is that there is not a monotonically dependence of the rate of the cyclotron energy with a magnetic field ∂E ∂H can be estimated to be for the first two Landau levels 0.17 meV /kOe.…”

Capture of carriers by screened charged centres and low-temperature shallow-impurity electric field breakdown in semiconductors

“…Screening induced µ(E) increase causes an additional (besides of n(E)) current increase in the avalanche-like region of the CVC. Note that it was already established from cyclotron resonance line shape investigations of n − GaAs that free carrier screening of charged impurities is strong at the breakdown electric fields [9][10].For LT-SIEFB there is no need for the condition r s = a * B , when total screening of impurity state occurs. First of all such a condition means all neutral shallow impurities to be ionized in semiconductor.…”