Precise tuning of the Curie temperature of (Ga,Mn)As-based magnetic semiconductors by hole compensation: Support for valence-band ferromagnetism

Abstract

For the prototype diluted ferromagnetic semiconductor (Ga,Mn)As, there is a fundamental concern about the electronic states near the Fermi level, i.e., whether the Fermi level resides in a well-separated impurity band derived from Mn doping (impurity-band model) or in the valence band that is already merged with the Mn-derived impurity band (valence-band model). We investigate this question by carefully shifting the Fermi level by means of carrier compensation. We use helium-ion implantation, a standard industry technology, to precisely compensate the hole doping of GaAs-based diluted ferromagnetic semiconductors while keeping the Mn concentration constant. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10 K is also confirmed in heavily compensated samples. Our experimental results are naturally explained within the valence-band picture.

Hole compensation effect in III-Mn-V dilute ferromagnetic semiconductors

“…The coercivity (HC) increases with increasing irradiation fluences, showing a maximum value about 284 Oe, and then decreases when the samples are rather heavily compensated. Similar results in He irradiated (Ga,Mn)As have been reported in our former work [12] where both TC and magnetization also decrease with increasing irradiation fluences. However, HC of He irradiated (Ga,Mn)As rises monotonically with increasing irradiation fluence.…”

“…Nevertheless, the essence of hole-mediated magnetization is not changed in (Ga,Mn)P, therefore the magnetization could be also tuned by compensation induced by ion irradiation as in for the magnetic easy axis (c) at 5 K versus DPA for (Ga,Mn)As (squares), (In,Mn)As (circles) and (Ga,Mn)P (triangles). Data of (Ga,Mn)As are taken from our former work [12].…”

p -type codoping effect in (Ga,Mn)As: Mn lattice location versus magnetic properties

“…5(d): all ZFC and FC curves, particularly under 200 Oe, exhibit a maximal value at around 15 K [39]. Interestingly, this is essentially different from (Ga,Mn)As with hole compensation or with much lower Mn concentration, where the reduction of TC is accompanied with the appearance of a blocking superparamagnetic phase [8,40,41]. It is well known, that in (Ga,Mn)As the super-exchange-interaction-induced antiferromagnetic coupling always occurs between the interstitial Mn atom (Mnint) and its nearest substitutional Mn atom (Mnsub) [1,16,42,43].…”

Charge Carrier Dynamics in Ga1-xMnxAs Studied by Resistance Noise Spectroscopy

“…By He-ion irradiation we tune the carrier density without changing the Mn content x of the film. In detail, the main effect of ion * corresponding author; e-mail: lonsky@physik.uni-frankfurt.de irradiation is the compensation of holes by introducing deep traps and thereby enhancing disorder, while both the concentration of substitutional Mn atoms and Mn interstitials remain unaltered [8]. A majority of the induced defects reside in the As sublattice [9].…”