Determination of free hole concentration in ferromagnetic Ga1−xMnxAs using electrochemical capacitance–voltage profiling

Abstract

We demonstrate that electrochemical capacitance voltage profiling can be used to determine the free hole concentration in heavily p-type doped low-temperature-grown GaAs films. This provides a simple and reliable method for measuring the hole concentration in ferromagnetic Ga 1-x Mn x As semiconductor alloys. The method overcomes the complications that arise from the anomalous Hall effect term which affects standard transport studies of carrier concentration in conducting ferromagnetic materials.Specifically, we find that the maximum Curie temperature of about 111 K found for our where N Mn is the concentration of uncompensated magnetic (Mn) spins that are coupled by indirect ferromagnetic interaction, p is the hole concentration, and C is a constant specific to the host material. It is seen from Eq.(1) that in order to increase T C one has to increase the concentration of uncompensated Mn ++ ions, N Mn , and/or the hole concentration, p. Alternatively, it has also been proposed that the ferromagnetic coupling between Mn ++ ions is mediated by holes localized on adjacent ions [6].Two key parameters common to most proposed models explaining the indirect fe rromagnetic coupling and predicting the Curie temperature in Ga 1-x Mn x As are the free hole concentration and the concentration of uncompensated Mn ++ ions [5,6]. One of the long standing problems impeding the analysis of these hole-mediated magnetic interactions that underlie the ferromagnetism in III-Mn-V semiconductor alloys has been the difficulty to reliably determine the hole concentration. The Hall effect which is commonly used to measure the concentration of charge carriers in semiconductors cannot be applied at normally available magnetic fields to materials like Ga 1- In this paper we show that the free hole concentration in ferromagnetic Ga 1-x Mn x As thin films can be reliably measured using the electrochemical capacitancevoltage (ECV) method. To demonstrate this, we first use ECV profiling to measure the hole concentration in a series of nonmagnetic p-type Ga 1-y Be y As layers grown by LT-MBE, and compare these results with Hall effect data obtained on the same samples. Additionally, valuable information has also been obtained from comparison of ECV andHall data observed on non-ferromagnetic Ga 1-x-y Mn x Be y As layers that were grown in conditions very similar to those used for the growth of ferromagnetic Ga 1-x Mn x As layers.The Ga 1-x Mn x As, Ga 1-y Be y As and Ga 1-x-y Mn x Be y As films were grown on semiinsulating (001) GaAs substrates in a Riber 32 R&D MBE system. Fluxes of Ga, Be and Mn were supplied from standard effusion cells, and As 2 flux was produced by a cracker cell. Prior to film deposition we grew a 450 nm GaAs buffer layer at 590ºC (i.e., under normal GaAs growth conditions). The substrate was then cooled down for the growth of a 3 nm thick low-temperature (LT) GaAs, followed by either a 110 nm Ga 1-x Mn x As layer, 4 or 230 nm thick layer of either Ga 1-y Be y As or Ga 1-x-y Mn x Be y As. The As 2 :Ga beam equival...

Electronic structure and carrier dynamics of the ferromagnetic semiconductorGa1−xMnxAs<

“…Also plotted in the inset is the Mn dependence of the ferromagnetic transition temperature, T C . The correlation between carrier density and T C , which has also been found in a number of measurements, [37][38][39][40] argues in favor of a pivotal role of the itinerant carriers in the formation of the ferromagnetic state.…”

Tight-binding model of spin-polarized tunnelling in (Ga,Mn)As-based structures

“…As TMR is primarily determined by spin polarization of the carriers at the Fermi level, the higher hole concentration the smaller is spin polarization at the Fermi level at given Mn spin polarization. For p = 3.5 × 10 20 cm −3 , which is the typical hole concentration in (Ga,Mn)As samples with a high Mn content [12], the TMR of about 250% is obtained. Because of self-compensation, the hole concentration depends rather weakly on x -thus, we have calculated the TMR for different x in the magnetic layers, while keeping the hole concentration constant, p = 3.5 × 10 20 cm −3 .…”

Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs

“…The quantitative determination of the superexchange constant J requires the knowledge of the energies of these virtual transitions, which are represented by the energy differences between the intermediate and initial states of the system of two ions and the completely filled valence bands, in the denominator of Equation (2). Of primary importance it is, however, to determine the sign of the superexchange interaction for the Mn Ga -Mn I pair.…”