Zn Epilayers Research Articles

Systematic and consistent ferromagnetism in InMnP:Zn bilayers for various Mn concentrations and annealing temperatures

The p-type InP:Zn epilayers were prepared by using metal-organic chemical vapor deposition, and Mn was subsequently deposited onto the epilayer by using molecular beam epitaxy. The p-type InMnP:Zn epilayers were annealed at relatively low temperatures of 200–350 °C and contained no secondary phases such as InMn, MnP, and MnO2, as verified by x-ray diffraction. However, minute presence of MnO2 was confirmed using transmission electron microscopy, which agreed with the magnetic properties measured by using a superconducting quantum interference device (SQUID). From the SQUID measurements, consistent and systematic ferromagnetic properties with clear ferromagnetic hysteresis loops were observed. The Curie temperature, TC, which persisted up to ∼ 180 K, was recorded depending on the Mn concentrations and annealing temperature. These results indicate that the ferromagnetic semiconductor InMnP:Zn can be fabricated at a very low annealing temperature without forming ferromagnetic precipitates except for MnO2.

Structural, optical, and magnetic properties related to p-type InMnP:Zn epilayers with curie temperatures of Tc1 ∼ 50 K and Tc2 ∼ 291 K

p-type InP:Zn epilayers were grown by using metalorganic chemical vapor deposition. After the growth of InP:Zn epilayers, Mn was evaporated on top of the InP:Zn epilayers by using a molecular beam epitaxy system. Then, Mn was diffused into the InP:Zn epilayers by annealing. InMnP:Zn epilayers were annealed at 600 °C for 60 s with Mn concentrations of both ∼1.5 and ∼3.0%. The optical transitions related to Mn appeared at 1.144, 1.187, and 1.212 eV and at 1.143, 1.179, and 1.205 eV for InMnP:Zn epilayers annealed at 600 °C for 60 s with Mn concentrations of ∼1.5 and ∼3.0%, respectively. Transitions related to Mn are noticeably activated due to an increase in the Mn concentration near 3.0% in comparison with transitions for Mn concentration near 1.5%. Clear ferromagnetic hysteresis loops were obtained for InMnP:Zn epilayers. The ferromagnetic hysteresis loop of the InMnP:Zn epilayers annealed with Mn concentration near 3.0% was bigger than that of epilayers with Mn concentration near 1.5%, and these results agree with the PL results that transitions related to Mn are remarkably activated upon annealing at Mn concentration near 3.0% in comparison with concentration near 1.5%. Ferromagnetic behavior persisted up Tc1 ∼ 50 K and Tc2 ∼ 291 K. Tc2 ∼ 291 K corresponds to MnP. Tc1 ∼ 50 K originates from intrinsic InMnP:Zn, which is caused by carrier-mediated ferromagnetism in the InMnP:Zn epilayer. We found that at Tc1 ∼ 50 K, a ferromagnetic semiconductor could be formed in a diluted magnetic semiconductor based on InMnP:Zn epilayers additionally co-doped with Zn.

Formation of the ferromagnetic semiconductor InMnP:Zn through low-temperature annealing by using Mn/InP:Zn bilayer

The ferromagnetic semiconductor p-InMnP:Zn epilayers were prepared through low-temperature annealing at 250 °C by using Mn/InP:Zn bilayers. The p-type InP:Zn epilayers were prepared by using metal-organic chemical vapor deposition. Then, ultra-thin Mn layers were subsequently deposited onto the layers by using molecular beam epitaxy. The Mn/InP:Zn bilayers were annealed at a low temperature of 250 °C in order to minimize the formation of precipitates such as InMn, MnP, Mn2P, and Mn3In. No ferromagnetic precipitates were observed in the annealed InMnP:Zn; however, the sample exhibited an antiferromagnetic phase of MnO2 that might have been formed because of an unavoidable surface oxide that had been created during the sample transfer. Despite the existence of antiferromagnetic MnO2, the samples revealed clear ferromagnetic hysteresis loops and showed high ferromagnetic transition temperatures up to ∼180 K. The results suggest that a ferromagnetic semiconductor InMnP:Zn can be effectively formed through low-temperature annealing by using a Mn/InP:Zn bilayer.

The structural, optical and magnetic properties and anomalous Hall effect of InMnP:Zn epilayers

The structural, optical, magnetic and magnetoelectrical transport properties of p-type InMnP:Zn (Mn: 0.019–0.290 at.%) epilayers, which had been prepared by thermal diffusion of Mn through molecular-beam-epitaxial deposition of Mn onto InP:Zn epilayers grown by metal-organic chemical vapor deposition and subsequent annealing of the samples, were systematically investigated. For analyses of structural properties, it was observed that the x-ray diffraction peaks of MnO2 for InMnP:Zn epilayers coincide with the P4/2/mmm structure of MnO2 proved by the electron diffraction analysis of transmission electron microscopy (TEM). For photoluminescence measurements, it was found that broad optical transitions related to Mn appear at 1.247 eV (Ev+0.173 eV) and 1.261 eV (Ev+0.159 eV), which are based on a band gap energy of 1.42 eV at 0 K. The samples revealed that in both the experimental pattern of TEM and the calculated diffraction pattern, {010} and {030} spots are missing, indicating that the FCC lattice was still maintained after the Mn doping. The forbidden, regularly spaced spots suggest the presence of a superlattice (a=11.738 Å), arising from the possible ordering of Mn atoms in the cubic structure of InP. The regularly spaced spots of ordered Mn produce the anomalous Hall effect (AHE) showing the characteristics of a diluted magnetic semiconductor (DMS), which is caused by hole-mediated ferromagnetism due to the increase of hole concentration in the tetrahedrally coordinated semiconductor. The transition from the ferromagnetic state to the paramagnetic state observed at ∼150 K in AHE measurements was confirmed to be almost consistent with the ferromagnetic transition temperature (TC) using superconducting quantum interference device measurements. These results suggest that an InP-based ferromagnetic semiconductor having relatively high TC can be successfully formed based on InMnP:Zn epilayers in a category of DMSs.

Comparison of annealing effects on Zn-doped GaMnAs and undoped GaMnAs epilayers

To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs:Zn) and undoped GaMnAs (u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 °C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 °C to 380 °C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T m close to the Curie temperatures T c was observed from the measurement of the temperature-dependent resistivity ρ( T) for both the GaMnAs:Zn and the u-GaMnAs samples. We found, however, that the maximum temperature T m observed for GaMnAs:Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs:Zn and MnAs or Mn–Zn–As complexes with increasing annealing temperature is most likely responsible for the differences in appearance.

Room-temperature ferromagnetism in Mn-N Co-doped p-ZnO epilayers by metal-organic chemical vapor deposition

Mn-N co-doped Zn epilayers were grown by metal-organic chemical vapor deposition. The Mn-N co-doped epilayers exhibit single phase hexagonal wurtzite structure, indicative of the small lattice damage from co-doping. Secondary ion mass spectroscopy analysis indicates that Mn and N atoms have been in situ incorporated into the ZnO epilayer. Hall measurements exhibit the conduction transition from n-type of the N mono-doped ZnO to p-type of the Mn-N codoped ZnO epilayer. This behavior is attributed to the low formation energy of Mn-N neighboring bonds in the co-doped epilayers. Mn doping leads to the low incorporation of N-H and N-N complexes, which are abundant in the N mono-doped epilayer and always act as compensation centers of holes. Moreover, room temperature ferromagnetism has been observed on the above co-doped epilayer, which is possibly due to the hole mediation on the ferromagnetic ordering of Mn atoms.

Relevant, systematic variation of morphology and magnetism according to annealing in InMnP:Zn

InMnP:Zn epilayers doped with Mn (0.290 at.%) were annealed at 723–873 K for 60 s and 473–573 K for 30 min. Using Auger electron spectroscopy, the changes in concentration profiles of the epilayers correlated to the ferromagnetic origin as a function of the annealing conditions. The epilayers annealed at 723–873 K for 60 s exhibited InMn 3 persisting up to 583 K. For InMnP:Zn epilayers annealed at 523–573 K for 30 min, the concentration depth profiles remained flat so that the stoichiometry was well maintained without precipitates such as InMn 3 and MnP comparable to the as-grown InP:Zn before doping Mn. These samples showed clear ferromagnetic hysteresis loops. Curie temperature was about 150 K. A ferromagnetic hysteresis loop was obtained even at very lower annealing temperature of 473 K.

Structural, Optical, and Magnetic Characteristics of an InMnP:Zn Epilayer

Structural, Optical, and Magnetic Characteristics of an InMnP:Zn Epilayer

Enhanced Curie temperature persisting between 100 and 200 K (∼50 K by theory) with Mn (∼0.290%) based on InMnP:Zn

The samples with the Mn concentrations of 0.290% and 0.062% revealed that both in the calculated diffraction pattern and experimental pattern of transmission electron microscopy (TEM), the FCC lattice was still maintained after the Mn doping. The regularly spaced spots of ordered Mn produce the anomalous Hall effect (AHE) showing the characteristics of diluted magnetic semiconductor, which is caused by hole-mediated ferromagnetism due to the increase of hole concentration in tetrahedrally coordinated semiconductor. Ferromagnetic semiconductor of T c between 100 and 200 K demonstrated by TEM and AHE can be formed in diluted magnetic semiconductor based on InMnP:Zn epilayers additionally co-doped with Zn.

Clarification of Mn–Zn interaction for InMnP:Zn epilayer by photoluminescence and x-ray photoelectron spectroscopy

Transition related to the Mn–Zn interaction was observed in photoluminescence (PL) study of the InMnP:Zn epilayer and the peak position blueshifted with increasing Mn concentration. X-ray photoelectron spectroscopy was used to clarify the blueshift of the PL peak. The binding energy shifts of Mn 2p and Zn 2p core levels indicative of the interaction between Mn and Zn were observed. This mutual interaction between Mn 2p and Zn 2p agrees with the result that the Mn-related transition in InMnP:Zn codoped with Zn is shifted to the higher energy region in comparison with InMnP without additional doping of Zn.

Characteristics of diluted magnetic semiconductor for p-type InMnP : Zn epilayer

p-type InP : Zn epilayers were prepared by metal-organic chemical vapor deposition and subsequently doped with Mn by heat treatment after evaporation of a thin film of Mn on top of the InP : Zn epilayer using a molecular-beam epitaxy system. No evidence of secondary phase formation such as MnP, MnIn, and MnZn within the InMnP : Zn epilayer was found, and single-phased InMnP : Zn epilayer was well formed. The results of photoluminescence measurements showed that the optical broad transitions related to Mn appeared near 1.187, 1.198, and 1.227 eV by the injection of Mn into the InP : Zn epilayer. Clear ferromagnetic hysteresis loops were observed at 10 K and the temperature-dependent magnetization of the sample with 3% Mn maintained the ferromagnetic behavior up to 370 K.

Diluted magnetic semiconductor of p-type InMnP:Zn epilayer

We investigated the characteristics of p-type InMnP:Zn epilayer using various measurements so as to compare its properties with those of bulk InMnP. InP:Zn epilayers of p-type were prepared by metal organic chemical vapor deposition and subsequently doped with Mn by heat treatment after the evaporation of Mn on top of InP:Zn epilayers using a molecular-beam epitaxy system. The samples were structurally characterized by X-ray diffraction. No evidence of secondary phase formation such as MnP, MnIn, and MnZn within the InMnP:Zn epilayer was found, and single-phase InMnP:Zn epilayer was well formed. The compositional results of energy dispersive X-ray peak displayed injected concentration of Mn near 1.5% and 3.0%. The results of photoluminescence measurement showed that optical broad transitions related to Mn appeared near 1.187, 1.198, and 1.227 eV by the injection of Mn into the InP:Zn epilayer. Clear ferromagnetic hysteresis loops were observed at 10 K and the temperature-dependent magnetization of the samples with the Mn concentration near 1.5% showed ferromagnetic behavior persisting upto 390 and 300 K and persisting upto 370 K for the sample near 3.0%. It is found that in this system the proper annealing temperature is 450 °C. p-type InMnP:Zn epilayers represent a ferromagnet with superior properties ( H c = 311 G , saturation magnetization M = 7.6 × 1 0 - 5 emu ) in comparison with InMnP:Zn bulk ( H c = 134 G , M = 4.1 × 1 0 - 5 emu )

Effect of donor-acceptor complex dissociation of the properties of the surface boundary region in P-InP:Zn during its thermal oxidation

The effect of thermal oxidation on the properties of the surface boundary region in p-InP:Zn epilayer is discussed. Thermal oxidation has been carried out at temperatures ranging from 100°C to 550°C. The free hole concentration in the bulk epilayer was in the range of 2–6 × 10 16cm −3. The analysis of the Schottky barrier capacitance voltage characteristics, the photoluminescence spectra and the differential spectra obtained from the thermally stimulated capacitance in Ag- p-InP Schottky diodes have shown that thermal oxidation in p-InP:Zn led to significant transformations of the parameters of the indium phosphide boundary region. The transformation covered changing of N a- N d profiles, variations of absolute values for concentrations of shallow and deep centres, variations of luminescence intensity and types of photoluminescence spectra. The observed effects were interpreted by a model designed to study the dissociation of neutral donor-acceptor Zn- V p, complexes in the space charge region surface of p-InP, provided the dissociation occurs under varying rates of the generation of phosphor vacancies in the boundary region.

Effect of growth parameters on the properties of GaN : Zn epilayers

The vapor-phase HCl/Ga/NH 3 method for deposition of GaN : Zn epilayers on sapphire substrates has been investigated to determine the dependence of epilayer resistivity, cathodoluminescence, and surface quality on the growth parameters. Both nucleation and control of the epilayer properties have been significantly improved by introducing HCl directly into the deposition zone in addition to the HCl that passes over the Ga source to produce GaCl. The effect of annealing on the stability of undoped layers and on the cathololuminescence of Zn-doped layers has also been investigated. Electroluminescent devices with reproducible properties have been obtained by growing structures consisting of an undoped n + layer, a Zn-doped n-type layer, and a very thin, Zn-doped, high-resistivity layer whose growth parameters determine the emission wavelength and electroluminescence efficiency.