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The effects of growth temperatures (in a wide range from 100 to 800 °C) on properties of a-plane (11 2 ¯ 0) ZnO films grown on r-plane (1 1 ¯ 02) sapphire substrates by plasma-assisted molecular beam epitaxy were investigated. The film was grown as polycrystalline at 100 °C, but grown as single crystalline at the temperatures from 200 to 800 °C without any mixture of c-plane (0001) ZnO and m-plane (10 1 ¯ 0) ZnO. The single crystalline ZnO films showed anisotropic surface morphology with the conglomerated granules or striations along the [0001]ZnO direction. The ZnO film grown at 400 °C showed better crystal quality than others. It showed the smallest full width at half maximums of 0.450° and 0.297° for (11 2 ¯ 0) x-ray omega rocking curves under the measuring configuration with the omega axis parallel and perpendicular to the ZnO and directions, respectively, and 0.387° for (10 1 ¯ 1) omega rocking curve. The threading dislocation and the stacking fault densities were determined to be ~ 3.7 × 1010 cm−2 and ~ 8.5 × 104 cm−1 for the ZnO film grown at 400 °C.

The measurements of the photoluminescence (PL) spectra have been performed on GaAs, GaMnAs, GaAs:Be, and GaMnAs:Be samples to study the effect of Be codoping on the PL spectra of GaMnAs layers grown via low temperature molecular beam epitaxy. Based on the temperature dependence of the exciton-related transitions energy, it was shown that doping GaAs with Mn and Be leads to modification of the temperature dependence of the band gap. It was shown that although Be itself weakly affected the PL spectra of GaAs, codoping with Be significantly modified the PL spectra of GaMnAs.

We investigated the structural properties of Zn-polar ZnO films with low temperature (LT) ZnO and MgO buffer layers grown by plasma-assisted molecular beam epitaxy on (0001) c-Al2O3 substrates using X-ray diffraction and transmission electron microscopy (TEM). The effects of MgO buffer layer thickness and LT ZnO buffer layer thickness were also examined. The optimum thicknesses for better crystal quality were 8 and 40 nm. One-pair and two-pair LT ZnO/MgO buffer layers were employed, and the changes in the structural properties of the high-temperature (HT) ZnO films using such buffer layers were studied. Contrary to the general tendency of c-ZnO films, the HT ZnO films on the LT ZnO/MgO buffer layers showed higher full width at half maximum (FWHM) values for X-ray rocking curves (XRCs) with (0002) reflection than those with (1011) reflection. Compared with the one-pair LT ZnO/MgO buffer layers, the FWHM values of (0002) XRCs markedly decreased, whereas those of (1011) XRCs slightly increased due to the insertion of one more pair of LT ZnO/MgO buffer layers into the previous film with one-pair LT ZnO/MgO buffer layers. The cross-sectional TEM observations with the two-beam condition confirmed that the screw dislocation was the dominant threading dislocation type—a finding that agreed well with the XRC results. On the basis of the plan-view TEM observations, the densities of the total threading dislocations for the HT ZnO films with the one- and two-pair LT ZnO/MgO buffer layers were determined as 2.3 × 109 cm− 2 and 1.6 × 109 cm− 2, respectively. The results imply that the crystal quality of Zn-polar ZnO films can be improved by two-pair LT ZnO/MgO buffer layers, and types of threading dislocations can be modified by adjusting the buffer system.

We have studied the electrical and magnetic properties of p-type semiconductor thin films of Si1 − xMnx/Si (x = 0.036 and 0.05) grown by molecular beam epitaxy. Experimental results reveal that the resistivity of the samples decreases gradually with increasing measurement temperature, which can be described well by Mott's variable-range-hopping model. All the samples exhibit the ferromagnetic ordering above room temperature. Among these samples, Si0.95Mn0.05 has a higher hole density and magnetization. This indicates an enhancement of hole-mediated ferromagnetic exchange interactions when the Mn-doping concentration is increased.

In this study, micro-porous poly(methyl methacrylate)-grafted polyethylene separators (PE-g-PMMA) were prepared by a radiation-induced graft polymerization of methyl methacrylate onto a conventional PE separator followed by a phase inversion. After the phase inversion, the micro-pores were generated in the grafted PMMA layer. The prepared micro-porous PE-g-PMMA separators showed an improved electrolyte uptake and ionic conductivity due to their improved affinity with a liquid electrolyte and the presence of pores in the grafted PMMA layer. The PE-g-PMMA separators exhibited a lower thermal shrinkage compared to the original PE separator. The PE-g-PMMA separators showed a better oxidation stability up to 5.0 V when compared to the original PE separator (4.5 V).

Amorphous _ semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to for 3 minutes in high vaccum chamber. The electrical and magnetotransport properties of as-grown and annealed samples have been studied. X-ray diffraction patterns analysis revealed that the samples still maintain amorphous state after annealling at for 3 minutes and they were crystallized when annealing temperature increase to . Temperature dependence of resistivity measurement implied that as-grown and annealed _ films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The -annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was 8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

다결정 Ge 1 ? x Mn x 박막의 자기적 상들에 관한 연구가 이루어졌다. Molecular beam epitaxy(MBE) 장비를 이용해 400 ℃에서 Ge 1 ? x Mn x 박막을 성장시켰다. Ge 1 ? x Mn x 박막의 캐리어 유형은 P타입 이였고, 전기 비저항 값은 4.0 × 10 ?2 ~1.5 × 10 ?4 ohm-㎝이었다. 자기적인 특성과 미세구조의 분석에 기초하여 Ge 1 ? x Mn x /SiO₂/Si(100) 박막에 310 K 이내의 큐리에온도를 지닌 강자성의 Ge₃Mn? 상이 형성되었음을 알 수 있었다. 게다가, Ge₃Mn? 상이 형성된 Ge 1 ? x Mn x 박막은 20 K, 9 T의 자기장에서 약 9 %의 음의 자기저항을 보였다.

Micro-porous polyethylene separator was modified by radiation grafting of methyl methacrylate in order to improve its affinity with a liquid electrolyte. The degree of grafting (DOG) increased with the monomer concentration and grafting time. The morphological change of the modified separator was investigated by scanning electron microscopy. The degree of crystallinity upon grafting was reduced due to the formation of an amorphous PMMA layer. The electrolyte uptake and the ionic conductivity of the separator increased with an increase in the DOG. The ionic conductivity reached 2.0 mS/cm for the grafted polyethylene separator with 127 wt% DOG.

Polystyrene-grafted poly(vinylidene fluoride) (PVDF-g-PS) membranes were prepared by simultaneous γ-irradiation-induced graft polymerization. The morphological changes of the prepared membranes were investigated by scanning electron microscopy. The degree of grafting (DOG) increased with increasing absorption doses. The degree of crystallinity upon grafting was found to decrease due to the formation of amorphous polystyrene layer. The grafted membranes showed better electrolyte uptake and retention ability compared to the ungrafted membrane. The ionic conductivity of the membrane with LiClO 4 /γ-butyrolactone-based electrolyte increased with the increase in the DOG and reached 2.50 mS/cm for the highest sample.

We report on the observation of p-type conductivity and ferromagnetism in diluted magnetic semiconductor (Zn 0.97 Mg 0.01 Mn 0.02 )O:P films grown on SiO₂/Si substrates by pulsed laser deposition. The p-type conduction with hole concentration over 1018 ㎝ ?3 is obtained by codoping of Mg and P followed by rapid thermal annealing in an O₂atmosphere. Structural and compositional analyses for the p-type (Zn 0.97 Mg 0.01 Mn 0.02 )O:P films annealed at 800 ℃ indicates that highly c-axis oriented homogeneous films were grown without any detectable formation of secondary phases. The films were found to be transparent in the visible range. The magnetic measurements clearly revealed an enhancement of room temperature ferromagnetism by p-type doping.

The transport properties of MnGaAs layers embedded with MnAs clusters have been investigated. It was demonstrated that the presence of MnAs clusters in GaMnAs matrix leads to appearance of photoconductivity and absorption current. These phenomena are related to carrier localization effects at the band bending in the vicinity of the cluster—matrix interface.

Photoluminescence (PL) measurements of the GaMnAs layers embedded with MnAs clusters have been performed. It was shown that the presence of MnAs clusters in the semiconducting matrix leads to appearance in the PL spectra a broad peak with local maximums at 1.36 and 1.33 eV, which are related with the defects generated in the phase separation process. The effect of the MnAs clusters on the temperature dependent band gap of GaMnAs was also observed.

The neutron irradiation effect of polycrystalline Si 1− x Mn x semiconductor thin films has been studied. The Si 1− x Mn x semiconductor thin films were grown on SiO 2 /(1 0 0)Si substrate at 400 °C by using a MBE. The as-grown specimens are irradiated by the fast neutrons of 0.82 MeV in a neutron research reactor at KAERI. After neutron irradiation, the electrical resistivities of neutron-irradiated specimens increase with the irradiation amount, while the saturation magnetizations decrease. Hall analysis reveals that the mobility of neutron-irradiated specimen decreases remarkably. The XRD and TEM analyses show that the phase transformation is not induced by the neutron irradiation.

Polycrystalline Ge 1− x Mn x thin films were irradiated with neutrons, and their electrical and magnetic properties have been investigated. As-grown specimens have p-type carriers and electrical resistivities are in the range of 1.3 × 10 −4 –5.2 × 10 −4 ohm cm at room temperature. After the irradiation of neutrons the carrier type is not changed, but the electrical resistivities increase with the amount of neutron irradiation. In addition, some of neutron-irradiated Ge 1− x Mn x thin films transform from the semiconductor characteristics into the metallic characteristics at low temperature. The saturation magnetizations of neutron-irradiated Ge 1− x Mn x thin films decrease, but the coercive forces increase with the irradiation amounts. The XRD analysis suggests that the defects generated by the neutron-irradiation cause the change of electrical and magnetic properties of Ge 1− x Mn x thin films exposed to neutron irradiation.

Amorphous Ge 1− x Mn x thin films were grown in order to expand the solubility limit of Mn. The amorphous Ge 1− x Mn x thin films were grown on (1 0 0)Si substrate at 373 K by using a thermal evaporator. The solubility of Mn in amorphous Ge 1− x Mn x thin films reaches up to 17 at.%. The amorphous Ge 1− x Mn x thin films are ferromagnetic and the T C is ∼150 K. The largest saturation magnetization of amorphous Ge 1− x Mn x thin films is ∼100 emu/cm 3 for x = 0.118 at 5 K. The variation of electrical resistivity with respect to temperature reveals that the amorphous Ge 1− x Mn x thin films have semiconductor characteristics. The in-field electrical resistivity of amorphous Ge 1− x Mn x thin films is lower than the zero-field electrical resistivity when T T C , but the reverse is true when T > T C . However, the in-field electrical resistivity of amorphous Ge 1− x Mn x thin films is always higher than the zero-field electrical resistivity when x > ∼12 at.%. Magneto-transport characteristics of amorphous Ge 1− x Mn x thin films show anomalous Hall phenomenon and negative magnetoresistance when T T C . The results suggest that the Mn atoms in amorphous Ge 1− x Mn x thin films be related to spin dependent scattering depending on magnetization.

The polycrystalline (Si1−xGex)1−yMny thin films have been grown by using MBE and investigated. In Si1−xMnx and Ge1−xMnx alloy, Ge3Mn5 and SiMn phases are representative strong ferromagnetic phases. Ge3Mn5 are mainly formed when Ge is rich, and SiMn are mainly formed when Si is rich. These formations of specific phases are provable from structure analysis by X-ray diffractometer (XRD) and measuring magnetic properties by magnetic properties measurement system (MPMS). At low Ge composition, saturation magnetization values and Curie temperature generally increase with Ge composition. Ferromagnetic properties of polycrystalline (Si1−xGex)1−yMny thin films near RT disappear when amounts of Si become over 70 at.% in Si1−xGex alloy because Ge3Mn5 phase that have Tc around 310 K cannot be formed. It is confirmed that structural analysis shows that Ge is incorporated interstitially in the SiMn phase structure with a lattice expansion with respect to the original compound. But, definite properties change can not be observed. Hall measurement shows that polycrystalline (Si1−xGex)1−yMny thin films have p-type. Temperature dependency resistivity of (Si1−xGex)1−yMny thin films behavior like metal. However, there exist some transition points in resistivity curve that are relation with Curie temperature of magnetic phases.

Doping characteristics of Mg and Be in GaN films grown using a new single GaN precursor via molecular beam epitaxy were investigated. X-ray diffraction analysis confirmed that the GaN lattice expands or contracts with Mg or Be doping due to their differences in the size with respect to Ga. The c -axis oriented growth mode has shifted to the basal-plane orientation as Mg increases. Semi-insulating electrical resistivities were observed in the as-grown films due to hydrogen passivation of the dopants. The major bonding configurations were Mg–H and Mg–H–Mg in GaN:Mg. However, Be–H–Be bonding was dominant over Be–H bonding in the GaN:Be films. The annealing behaviors of the films were different between GaN:Mg and GaN:Be films. They were discussed with the different passivation bonding configurations.

Magnetotransport is a prerequisite to realization of electronic operation of spintronic devices and it would be more useful if realized at room temperature. The effects of Be codoping on GaMnAs on magnetotransport were investigated. Mn flux was varied for growth of precipitated GaMnAs layers under a Be flux for degenerate doping via low-temperature molecular beam epitaxy. Magnetotransport as well as ferromagnetism at room temperature were realized in the precipitated GaAs:(Mn,Be) layers. Codoping of Be was shown to promote formation of MnGa clusters, and annealing process further stabilized the cluster phases. The room-temperature magnetic properties of the layers originate from the ferromagnetic clusters of MnGa and MnAs embedded in GaAs. The degenerately doped metallic GaAs matrix allowed the visualization of the magnetotransport through anomalous Hall effect.

We report hole-induced ferromagnetism in diluted magnetic semiconductor Zn_(0.99)Mn_(0.01)O films grown on SiO₂/Si substrates by reactive sputtering. The p-type conduction with hole concentration over 10^(18) ㎝-³ is achieved by P doping followed by rapid thermal annealing at 800 ℃ in a N₂ atmosphere. The p-type Zn_(0.99)Mn_(0.01)O:P is carefully examined by x-ray diffraction and transmission electron microscopy. The magnetic measurements for p-Zn_(0.99)Mn_(0.01)O:P clearly reveal ferromagnetic characteristics with a Curie temperature above room temperature, whereas those for n-Zn_(0.99)Mn_(0.01)O:P show paramagnetic behavior. The anomalous Hall effect at room temperature is observed for the p-type film. This result strongly supports hole-induced room temperature ferromagnetism in p-Zn_(0.99)Mn_(0.01)O:P.

We have investigated the effects of Al codoping on the structural, electrical transport, and magnetic properties of oxide diluted magnetic semiconductor thin films prepared by reactive sputtering. Nondoped thin films show semiconducting transport behavior and weak ferromagnetic characteristic. The Al doping increases the carrier concentration and results in an decrease of resistivity and metal-insulator transition behavior. With increasing carrier concentration, the magnetic properties drastically change, exhibiting a remarkable increase of the saturation magnetization. These results show carrier-enhanced ferromagnetic order in Cr-doped ZnO.

Magnetic properties of amorphous Ge 1− x Mn x thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge 1− x Mn x thin films are 5.0×10 −4 ∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge 1− x Mn x thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80–160 K, and saturation magnetization is 35–100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge 1− x Mn x thin films have p-type carrier and hole densities are in the range from 7×10 17 to 2×10 22 cm −3 .

A thermoelectric flow sensor for small quantity of gas flow rate was fabricated using silicon wafer semiconductor process and bulk micromachining technology. Evanohm R alloy heater and chromel-constantan thermocouples were used as a generation heat unit and sensing parts, respectively. The heater and thermocouples are thermally isolated on the laminated membrane. The characteristics of this sensor were observed in the flow rate range from 0.2 slm to 1.0 slm and the heater power from 0.72 mW to 5.63 mW. The results showed that the sensitivities : voltage difference, : flow rate) were increased in accordance with heater power rise and decreasing of flow rate.

The necessity for employing a low substrate temperature for MnAs growth in molecular beam epitaxy has been clarified through an investigation for the effect of the growth temperature on the microscopic structural morphology. The atomic registry of MnAs films on GaAs substrate was examined by transmission electron microscopy. The MnAs films revealed a single-crystalline nature at ∼300 °C, but the morphology changed to polycrystalline with an increase in the substrate temperature. The variation in the degree of the magnetic anisotropy of the films was consistent with the change of the film morphology along with the substrate temperature. The uniaxial in-plane magnetic anisotropy of the epitaxial MnAs film was correlated with the surface reconstruction on the GaAs substrate.

Be-codoped GaMnAs layers were systematically grown via molecular beam epitaxy with varying Mn- and Be-flux. Mn flux was controlled to cover from solid solution type GaMnAs to precipitated GaMnAs. Two Be flux were chosen to exhibit semiconducting and metallic resistivity in the grown layers. The structural, electrical, and magnetic properties of GaAs:(Mn, Be) were investigated. The lightly Be-codoped GaMnAs layers showed ferromagnetism at room temperature, but did not reveal magnetotransport due to small magneto-resistance and high resistance of the matrix. However, room temperature magnetotransport could be observed in the degenerate Be-codoped GaMnAs layers, and which was assisted by the high conductivity of the matrix. The Be-codoping has promoted segregation of new ferromagnetic phase of MnGa as well as MnAs.

MBE-grown poly Ge1−xMnx/SiO2/(1 0 0)Si semiconductor thin films were annealed, and magnetic properties of the annealed semiconductors have been studied. As-grown poly Ge1−xMnx semiconductor has p-type carriers and electrical resistivity is in the range of 4.0×10−3–0.5×10−3 Ω cm at room temperature. The carrier type is not changed during annealing, but the electrical resistivity increases with annealing temperature and time. During annealing Ge3Mn5 ferromagnetic phase transforms into Ge8Mn11 anti-ferromagnetic phase and then the Ge8Mn11 phase is decomposed into Ge, β-Mn and some unidentified phases.

MBE-grown polycrystalline Si 1-x Mn x semiconductors were aged at 700°C for various times, and heat treatment effect on the magnetic properties was studied. Extensive analyses on the magnetization characteristics and microstructure of polycrystalline Si 1-x Mn x semiconductors reveal that ferromagnetic MnSi and anti-ferromagnetic Mn 5 Si 3 phases are transformed into ferromagnetic Mn 4 Si 7 , nonmagnetic Mn 5 Si 2 , anti-ferromagnetic β-Mn and unidentified minor phases. The phase transformation causes the decrease of saturation magnetizations after heat treatment.

Polycrystalline Si 1− x Mn x semiconductor thin films were grown on SiO 2 /(1 0 0)Si substrates at 400°C using a molecular beam epitaxy, and their magnetic and electrical properties have been studied. The polycrystalline Si 1− x Mn x semiconductor has p-type carriers and electrical resistivity is 2.0×10 −4 –1.3×10 −3 Ω cm at room temperature. Saturation magnetization increases with Mn concentration and reaches a maximum of 12.8 emu/cm 3 at Mn 28.8 at%. Magnetization characteristics and X-ray analysis reveal the ferromagnetic SiMn phase and the anti-ferromagnetic Si 3 Mn 5 phase are the major magnetic phases formed in the polycrystalline Si 1− x Mn x semiconductors.

GaMnN and Mg-codoped GaMnN films were grown via molecular beam epitaxy using the GaN single precursor Et 2 Ga(N 3 )NH 2 C(CH 3 ) 3 . Through a comparative study, it was confirmed that hole carriers mediate ferromagnetism in GaMnN at room temperature. Furthermore, the effects of Mg codoping on the conductivity and magnetization properties of the layers were investigated. Mn in GaN is shown to be inefficient as a dopant in generating itinerant carriers and this limits the saturation magnetization. On the other hand, Mg revealed higher efficiency in producing holes, and as a consequence could greatly enhance the magnetization via increased ferromagnetic coupling among Mn atoms. The results suggest that the magnetic ordering can be adjusted by separate control of the carrier concentration and the content of the magnetic element in films of III-V ferromagnetic semiconductors.

GaMnN magnetic thin films were grown using a single GaN precursor of Et2Ga(N3)NH2C(CH3)3, and their structural and magnetic properties were investigated. The GaN layers were grown with c-axis texture orientation. The films, however, revealed a great improvement in the crystallinity upon in-situ and ex-situ annealing at higher temperatures. Incorporation of Mn, however, randomized the growth direction as revealed by investigations of X-ray diffraction and transmission electron microscopy. For high Mn flux, a cubic second phase, Mn3GaN, has precipitated. It is a structure seldom observed in other conventional molecular beam epitaxy growth. It, however, offered a high conductivity to the GaMnN matrix. The precipitated films showed a uniaxial anisotropy in the magneto-transport. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The behavior of precipitates in magnetic GaMnN films upon annealing was investigated. The major precipitate was Mn3GaN phase in GaMnN layers grown via molecular beam epitaxy using a single GaN precursor under high Mn flux. With heat treatment of the films, the Mn3GaN phase decomposed and a part of it was converted to magnetic Mn3Ga phase through detachment of nitrogen. The decomposition kinetics was further accelerated by neutron irradiation, which generated defects in the lattice and assisted the decomposition of the precipitates. The saturation magnetization of the homogeneous GaMnN layer was increased after the heat treatment while it was decreased in the precipitated GaMnN layer. The increase and decrease of the magnetization of the heat-treated GaMnN films was explained consistently by the role of the precipitates in the films. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the synthesis of spinel oxide ZnCo2O4 thin films and the effects of the oxygen partial pressure in the sputtering gas mixture on their electrical and magnetic properties. The conduction type and carrier concentration were found to be dependent on the oxygen partial pressure ratio: n-type and p-type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. A ferromagnetic coupling was observable in p-type ZnCo2O4, whereas an antiferromagnetic interaction was found for insulating and n-type ZnCo2O4 film, revealing hole-mediated ferromagnetic transition in ZnCo2O4. Arrott plot analysis of magnetization data at 5 K also indicated non-zero spontaneous magnetization for p-type ZnCo2O4. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the transport and magnetic properties of Mn-doped CuAlO2 ceramics (CuAl1−xMnxO2, 0 ≤ x ≤ 0.05) fabricated by standard solid solution method in an air atmosphere at a sintering temperature of 1150 °C. The equilibrium solubility of Mn ions in CuAlO2 was found to be as low as 3 mol%. Non-doped CuAlO2 ceramics were semiconducting with a hole concentration of ∼5.8 × 1016 cm−3 and an increase of Mn ion rapidly reduced the hole concentration. The magnetization measurements for all CuAl1−xMnxO2 samples showed paramagnetic behaviors and a negative value of the Curie–Weiss temperature corresponding to antiferromagnetic exchange coupling between Mn ions in delafossite CuAlO2 lattice. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the effect of the oxygen partial pressure ratio in the sputtering gas mixture on the electrical and magnetic properties of cubic spinel ZnCo2O4 thin films grown by reactive magnetron sputtering. The conduction type and carrier concentration in ZnCo2O4 films were found to be dependent on the oxygen partial pressure ratio. The maximum electron and hole concentration at 300 K were estimated to be as high as 1.37 × 1020 cm-3 and 2.81 × 1020 cm-3, respectively. While an antiferromagnetic coupling was found for n-type ZnCo2O4, a ferromagnetic interaction was observable in p-type ZnCo2O4, indicating hole-induced ferromagnetic transition in spinel ZnCo2O4.

We report on the growth of cubic spinel ZnCo2O4 thin films by reactive magnetron sputtering and bipolarity of their conduction type by tuning of oxygen partial pressure ratio in the sputtering gas mixture. Crystal structure of zinc cobalt oxide films sputtered in an oxygen partial pressure ratio of 90% was found to change from wurtzite Zn1−xCoxO to spinel ZnCo2O4 with an increase of the sputtering power ratio between the Co and Zn metal targets, DCo/DZn, from 0.1 to 2.2. For a fixed DCo/DZn of 2.0 yielding single-phase spinel ZnCo2O4 films, the conduction type was found to be dependent on the oxygen partial pressure ratio: n-type and p-type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. The electron and hole concentrations for the ZnCo2O4 films at 300 K were as high as 1.37×1020 and 2.81×1020 cm−3, respectively, with a mobility of more than 0.2 cm2/V s and a conductivity of more than 1.8 S cm−1.

Anisotropy magneto-resistance and planar Hall-effect of ferromagnetic GaMnAs epitaxial films were investigated. The films were grown on 2 o off-cut GaAs (001) substrate in an optimized growth condition via low temperature molecular beam epitaxy. The GaMnAs layer revealed an easy axis along the (2x4) reconstruction direction of the substrate or along the off-cut direction. The large value of the anisotropy magneto-resistance ratio of ~7 % was realized by a well-alignment of the easy axis of the homogeneous ferromagnetic GaMnAs layer with the current. It also gives a very high planar Hall resistance ratio of ~500 %.

A thin-film multijunction thermal converter was fabricated through the process using 6 inch silicon wafer semiconductor process and bulk micromachining. Evanohm R alloy and chromel-constantan were used as a heater and thermocouple materials, respectively. The temperature coefficient of resistance of Evanohm R heater was about 75.12 ppm/ and the voltage sensitivity of the thermal converter indicated about 5.75 mV/mW in air. The transfer differences, measured by FRDC-DC method in the frequency range from 20 Hz to 10 kHz, showed the value under about 1.36 ppm, 0.83 ppm for the film thickness of 500, 200 nm, respectively. And in case of a 200 nm-thick thermal converter, the AC-DC transfer differences seems to be stabilized below the value of 1 ppm in the frequency range from 1 kHz to 500 kHz.

We have fabricated Zn0.75Co0.25O thin films on sapphire (0001) substrates at different substrate temperatures (400–700 °C) in a fixed O2 pressure of 1×10−5 Torr using pulsed laser deposition technique and investigated their structural and magnetic properties in relation to the growth conditions. X-ray diffraction and transmission electron microscopy observations have revealed that hexagonal Co clusters are present in the films grown at 700 °C. At relatively low temperatures (400–600 °C), homogeneous alloy films of wurtzite structure are formed with an epitaxial relationship of (0001)ZnCoO∣∣(0001)sap and [01 1 0]ZnCoO∣∣ 1 2 1 0]sap, which is the same as that for ZnO grown on (0001) sapphire. Observed results of the structural and magnetic properties collectively imply that the presence of the ferromagnetic Co clusters leads to ferromagnetism in Co-doped ZnO films.

We have characterized Zn1−xCoxO (x=0.25) films grown on sapphire (0001) substrates by pulsed laser deposition using various growth conditions to investigate the growth condition dependence of properties of Co-doped ZnO films. The substrate temperature (TS) was varied from 300 to 700 °C and the O2 pressure (PO2) from 10−6 to 10−1 Torr. When TS is relatively low (≲600 °C), homogeneous alloy films with a wurtzite ZnO structure are grown and predominantly paramagnetic, whereas inhomogeneous films of wurtzite ZnO phase mixed with rock-salt CoO and hexagonal Co phases form when TS is relatively high and PO2 is fairly low (≲10−5 Torr). The presence of Co clusters leads to room temperature ferromagnetism in inhomogeneous films. The temperature dependence of the magnetization for the homogeneous Zn1−xCoxO (x=0.25) films shows spin-glass behavior at low temperature and high temperature Curie–Weiss behavior with a large negative value of the Curie–Weiss temperature, indicating strong antiferromagnetic exchange coupl...

We present a detailed growth optimization procedure and experimental results for the growth of GaMnAs magnetic semiconductors in low-temperature molecular beam epitaxy. They were explored by using in-situ monitoring of the surface reconstruction patterns, double crystal/high-resolution x-ray diffraction, conductivity measurement, and superconducting quantum interference device measurements. The results showed strong correlations among the measurements. The room temperature conductivity measurement, in particular, was found to be a useful tool in forecasting the ferromagnetic transition temperature of the films. High quality GaMnAs films could contain Mn up to ≈5% without MnAs segregation at substrate temperatures of 215–275°C. The highest transition temperature of 80 K, however, was measured from the sample with 3.7% Mn grown at the substrate temperature of 250°C and As4 pressure of 1.4×10−6 torr for a growth rate of 0.25 μm/hr.

We report on the electrical and magnetic properties of Mn-doped ZnO, Zn 1 m x Mn x O, ceramics prepared by a solid-state reaction method. X-ray diffraction analysis shows that the Mn ion can be dissolved into ZnO up to ∼20 mol% without changing the wurtzite structure. We find from Hall measurements for Zn 1 m x Mn x O with an additional doping of 1 mol% Ga that the Mn doping in ZnO decreases electrical conductivity along with carrier concentration. For our ceramics, electrical resistivity decreases with increase of temperature, showing semiconducting behavior. We examine the temperature dependence of the magnetization for both field cooling and zero-field cooling.

GaMnAs and Be-codoped GaMnAs films grown via molecular beam epitaxy (MBE) were heat treated and the stability of Mn in the matrix was investigated. MnAs had a stable phase at the low growth temperature, but MnGa was stable at the annealing temperature. Be-codoping did not prevent the precipitation processes, but Be itself was stable during the annealing process to maintain the GaAs matrix at the high conductivity.

Effect of the phase segregation process on the transport properties of GaMnAs has been investigated. It was shown that the change of the transport properties in precipitated GaMnAs is not only the result of the decreasing Mn concentration in the semiconductor matrix, but the carriers’ localization effect in the vicinity of the cluster–matrix interfaces as well.

Si 1− x Mn x ( x ⩽ 0.22 ) thin films were grown by using a thermal evaporator, and their magnetic and electrical properties were investigated. The Si 1− x Mn x semiconductors are amorphous when Mn concentration is 9.0 at% and less. The electrical resistivities of amorphous Si 1− x Mn x ( x ⩽ 0.09 ) semiconductor thin films are in the range of 9.86–6.59×10 −4 Ω cm at room temperature and decrease with increasing Mn concentration. The amorphous Si 1− x Mn x ( x ⩽ 0.09 ) semiconductor thin films are p-type and hole densities are 3.73×10 18 –1.33×10 22 cm −3 at room temperature. Low temperature magnetization characteristics reveal that amorphous Si 1− x Mn x ( x ⩽ 0.09 ) semiconductor thin films are paramagnetic.

Amorphous Ge 1− x Cr x thin films are deposited on (1 0 0)Si by using a thermal evaporator. Amorphous phase is obtained when Cr concentration is lower than 30.7 at%. The electrical resistivities are 1.89×10 −3 –0.96×10 2 Ω cm at 300 K, and decrease with Cr concentration. The Ge 1− x Cr x thin films are p-type. The hole concentrations are 5×10 16 –7×10 21 cm −3 at 300 K, and increase with Cr concentration. Magnetizations are 7.60–1.57 emu/cm 3 at 5 K in the applied field of 2 T. The magnetizations decrease with Cr concentration and temperature. Magnetization characteristics show that the Ge 1− x Cr x thin films are paramagnetic.

GaMnN and Be-codoped GaMnN were grown via molecular beam epitaxy using a single GaN precursor and their structural and magnetic properties were examined. X-ray diffraction and superconducting quantum interference device (SQUID) measurements revealed that the grown layers are homogeneous without precipitates. The saturation magnetization of GaMnN has increased from ∼4 to ∼16 emu/cm3 via codoping of Be. The d–d exchange interaction between Mn atoms was discussed for the ferromagnetism of GaMnN.

We report on the structural, magnetic, and magnetotransport characteristics of Cr-doped indium tin oxide (ITO) films grown on SiO 2 /Si substrates by pulsed laser deposition. Structural analysis clearly indicates that homogeneous films of bixbyite structure are grown without any detectable formation of secondary phases up to 20 mol% Cr doping. The carrier concentration is found to decrease with Cr ion addition, displaying a change in the conduction type from n-type to p-type around 15 mol% Cr doping. Room temperature ferromagnetism is observed, with saturation magnetization of ∼0.7 emu/cm 3 , remnant magnetization of ∼0.2 emu/cm 3 and coercive field of ∼30 Oe for 5 mol% Cr-doped ITO. Magnetotransport measurements reveal the unique feature of diluted magnetic semiconductors, in particular, an anomalous Hall effect governed by electron doping, which indicates the intrinsic nature of ferromagnetism in Cr-doped ITO. These results suggest that Cr-doped ITO could be promising for semiconductor spin electronics devices.

We report on the growth of spinel ZnCo2O4 films using reactive magnetron sputtering and their electrical and magnetic properties, with particular emphasis on the relation of Curie–Weiss temperature (TCW) and conduction type. The conduction type and carrier concentration in these films were found to be dependent on the oxygen partial pressure ratio in the sputtering gas mixture. The highest electron and hole concentration at 300 K were 1.37×1020 and 2.81×1020 cm−3, respectively. A ferromagnetic coupling (TCW>0) was observable in p-type ZnCo2O4, whereas an antiferromagnetic interaction (TCW