p -type conductivity in cubic (Ga,Mn)N thin films

Abstract

The electrical and magnetic properties of p-type cubic (Ga,Mn) IntroductionThe emerging field of semiconductor spintronics relies on the ability to manipulate the electron spin in a semiconductor device, thus offering new prospects for non-volatile high speed information storage and processing. An important milestone in this field was the discovery of carrier-mediated ferromagnetism in III-V compounds doped with Mn [1]. Intensive efforts have since led to ferromagnetic transition temperatures T C in excess of 150K in (Ga,Mn)As [2,3,4], and an impressive range of prototype devices [5,6,7]. However, for widespread technological usage of these systems, a T C significantly above 300K is necessary, which may yet require the development of new materials.In this context, the Zener mean-field model prediction of room temperature ferromagnetism in (Ga,Mn) , a value significantly higher than the highest hole concentrations so far obtained in GaN. Furthermore, optical measurements have indicated that the Mn acceptor level lies over 1eV above the valence band maximum in Wurtzite (Ga,Mn)N [9,10], which is in agreement with density-of-states calculations [11]. Therefore, in contrast to the case for (Ga,Mn)As, Mn does not appear to be an efficient acceptor in Wurtzite GaN, and may not be expected to interact strongly with delocalised charge carriers in the conduction or valence bands. In spite of this, there are numerous observations of room temperature ferromagnetism in n-type (Ga,Mn)N, even in cases where no secondary phases have been identified [12]. The origin of the ferromagnetism in these cases is unresolved, but no conclusive evidence for a coupling between magnetic and semiconductor properties has been demonstrated, and it appears that this effect lies outside the Zener model prediction.It may be expected that Mn incorporation is favoured in the metastable zincblende (cubic) phase of GaN, since MnN is itself cubic with a similar lattice constant to GaN. at room temperature [14]. Cubic (Ga,Mn)N may therefore be a more promising candidate than the Wurtzite phase for room temperature carrier-mediated ferromagnetism. It is important to determine the origin of the p-type conductivity and investigate the nature of the Mn state in this material. Here we report on a detailed study of the electrical and magnetic properties of cubic (Ga,Mn)N films grown on GaAs(001) by molecular beam epitaxy. Growth and structureUndoped cubic GaN films and cubic (Ga,Mn)N layers were grown on semi-insulating GaAs (001) substrates by plasma-assisted molecular beam epitaxy (PA-MBE) using arsenic as a surfactant to initiate the growth of cubic phase material [15]. Films where grown under Nrich conditions, which has been found to be necessary for the effective substitutional incorporation of Mn in hexagonal (Ga,Mn)N [16]. The substrate temperature was measured using an optical pyrometer. Growth temperatures from 450 to 680 o C were used. The active nitrogen for the growth of the group III-nitrides was provided by an CARS25 RF activated plasma source...

High Temperature Ferromagnetism and Nano-Scale Phase Separations in Diluted Magnetic Semiconductors and Oxides

“…In addition to (Ga,Mn)As, (Zn,Mn)Te:N, and related systems, recent indications of ferromagnetism in p- (Ga,Mn)N [98,99] and p-(Ga,Mn)P [100], appear to support the conclusion about the importance of delocalized or weakly localized carriers in mediating efficient spin-spin interactions. However, in those and other experimentally relevant cases, non-uniformity associated with hole localization, and perhaps with competing ferromagnetic and antiferromagnetic interactions, is seen to affect strongly ferromagnetic properties.…”

Theory of ferromagnetic (III,Mn)V semiconductors

“…Reports of ͑Ga,Mn͒N epilayers synthesized in cubic and hexagonal crystal structures, of p-type and n-type ferromagnetic ͑Ga,Mn͒N, and of multiple ferromagnetic phases in one material all add to the complex phenomenology of these wide-gap DMSs ͑Korotov et al, 2001;Graf et al, 2002;Graf, Gjukic, et al, 2003;Arkun et al, 2004;Edmonds, Novikov, et al, 2005;Hwang et al, 2005;Sawicki, Dietl, et al, 2005͒. Uncertainties apply also to the interpretation of ferromagnetism seen in the ͑Ga,Mn͒P samples studied to date, which have been prepared by post-MBE ion implantation of Mn followed by rapid thermal ͑Theodor-opoulou et al., 2002;Poddar et al, 2005͒ or pulse-lasermelting annealing ͑Scarpulla et al, 2005͒. Experiments in these materials have not yet established unambiguously the nature of magnetic interactions in the ͑III, Mn͒P compounds.…”

Electron-electron and electron-phonon correlation effects on the finite-temperature electronic and optical properties of zinc-blende GaN

“…One of the approaches to eliminate these internal fields is the utilization of metastable non polar zinc-blende (zb) structures. It has also been reported that zb group IIInitrides have a quantum confined Stark effect in lowdimensional heterostructures 6 , high p-type conductivity in (Ga,Mn)N thin films 7 and negative differential resistance (NDR) at the resonant tunneling diode of the cubic Al(Ga)N/GaN 8,9 . Consequently a lot of interest is constantly attracted by this family of materials.…”