Positive Identification of theCr4+→Cr3+<

Abstract

Temperature-dependent Hall-effect measurements on two Cr-doped GaAs samples show a dominant center at E\-0.324-1.4X 10~4T eV, with respect to the valence-band edge. By comparison with secondary-ion mass spectroscopy measurements of the Cr concentration, and recent E PR measurements of the Cr 2+ , Cr 3+ , and Cr 4+ concentration in several samples, it is shown unambiguously that this energy describes the Cr 4+ -*Cr 3+ transition. This is the first conclusive evidence for a charge-state transition involving Cr 4+ in GaAs.

Ca2+‐Doped LaCrO3: A Novel Energy‐Saving Material with High Infrared Emissivity

“…Therefore, to maintain the electrovalence equilibrium, the Cr 3+ ions at the B sites transformed into Cr 4+ ions and formed electron holes, thus forming a p‐type semiconductor . The Ca 2+ doping introduced an impurity energy level of Cr 4+ in the LaCrO 3 forbidden gap, exhibiting a Cr 3+ ↔ Cr 4+ polaron hopping with activation energy of 0.32 eV . Its corresponding maximum excitation wavelength (λ) was estimated as 3.9 μm from the equation λ = hc/E a , where h is Planck's constant, c is speed of light, and E a is activation energy of electron hopping between Cr 3+ and Cr 4+ ions.…”

Electrical characterisation of (Ga,Mn,Cr)As thin films grown by molecular beam epitaxy

“…[16]). The neutral state Cr 3þ ð3d 3 Þ thereby acts as a hole trap, in which the transition Cr 4þ to Cr 3þ + hole (valence band) requires an energy of 0.32 eV [16].…”

“…[16]). The neutral state Cr 3þ ð3d 3 Þ thereby acts as a hole trap, in which the transition Cr 4þ to Cr 3þ + hole (valence band) requires an energy of 0.32 eV [16]. We believe that the Cr 3þ =Cr 4þ level (or impurity band) could account for the strong reduction of the hole density in the Cr-doped samples.…”

Optical Absorption of Cr4+ in GaAs:Cr

“…The thermal excitation energy of the Cr4+ + Cr3+ transition has been found to be Eth = 0.30 eV (extrapolated to T = 80 K) from TDH experiments [8] on p-GaAs: Cr4+. Therefore, the optical spectrum should be due to the photoionization transition…”

“…However, the spectral shape of this Cr4+ optical absorption in the spectral region 0.75 eV up to the GaAs absorption edge remained unknown because of the superposition with the absorption due to Cr3+ and Cr2+. Another important result was the identification of the Cr4+ --+ Cr3+ thermal transition from temperature-dependent Hall-effect measurements on p-type GaAs : Cr : Zn by Look et al [8] providing the thermal excitation energy of Cr4+ with respect to the valence band.…”