Electronic- and band-structure evolution in low-doped (Ga,Mn)As

Abstract

Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic-and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gaptransition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with ntype conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediated ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.

Band-gap narrowing in Mn-doped GaAs probed by room-temperature photoluminescence

“…Both the concentration dependence and the red-shift of the peak position with temperature establish direct evidence that Mn strongly affects the VB in the (Ga,Mn)As alloy, even for low Mn concentrations (<1 at.%), which is in contrast to the IB model where the Mn doping has little influence on the VB edge [31]. An interesting study has been recently reported by Yastrubchak et al, who investigated LT-MBE Ga 100%-x Mn x As samples with a nominal concentration of Mn up to 1.2 at.% by modulation photoreflectance spectroscopy [16]. They have shown that already 0.001 at.% of Mn influences the electronic structure of GaAs and that the IB merges with the VB for a Mn concentration higher than 0.005 at.%, although the Ga 100%-x Mn x As layer shows n-type conductivity due to the high-concentration of arsenic antisites As Ga .…”

“…The point of the debate is whether insulator to metal transition occurs in the merged valence and impurity bands (VB model) or in the still detached but well resolved impurity band (IB model) [6,12]. According to the VB model the valence band edge should merge with the Mn impurity band which was indirectly illustrated in various experiments [13][14][15][16][17] and justified by theoretical calculations [11]. By adapting the tight-binding Anderson approach and full-potential local-density approximation +U calculations, J.…”

Site-specific atomic order and band structure tailoring in the diluted magnetic semiconductor (In,Ga,Mn)As

“…Similarly, very diluted (In,Ga,Mn)As is n-type, too. The threshold Mn concentration between n-and p-type conduction depends on the actual concentration of As Ga donors and therefore on the actual MBE chamber set up and the growth conditions [47]. With further increase of Mn concentration, the CPPM mode starts to dominate the spectra, simultaneously with its energy shifted toward the TO-phonon line.…”

Band structure evolution and the origin of magnetism in (Ga,Mn)As: From paramagnetic through superparamagnetic to ferromagnetic phase

“…It provides an improvement in the accuracy over our earlier photoreflectance studies performed at room temperature. [26][27][28][29] LT-PR offers also an advantage over other optical methods applied to (Ga,Mn)As [30][31][32][33][34] where the optical response from the gap may be quenched by defects and is marred by the hole plasma. Importantly, the method allows to probe the valence-to-conduction band optical transitions regardless of the Fermi level location within the gap.…”

“…Similarly, very diluted (Ga,Mn)As is n-type too, as shown for a comparable set of samples characterized by thermoelectric power measurements. 28 A threshold Mn concentration bordering n and p-type materials depends on the actual concentration of As Ga donors and so on the actual MBE chamber set up and the growth conditions. In the case of the present set of samples about 0.3% of Mn was needed to form the CPPM band in the Raman spectra, indicating that around this concentration of Mn (Ga,Mn)As turns p-type.…”