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Schottky contact formation on p-GaN using W2B/Pt/Au and W2B5/Pt/Au metallization schemes was investigated using x-ray photoelectron spectroscopy (XPS), current-voltage (I-V), and Auger electron spectroscopy measurements. The Schottky barrier height (SBH) determined from XPS is 2.71 eV and 2.87 eV for as-deposited W2B- and W2B5-based contacts, respectively. By comparison, fitting of the I-V curves using the thermionic field emission model gives unphysical SBHs > 4 eV due to the presence of an interfacial layer acting as an additional barrier to carrier transport. Upon annealing to ∼600–700°C, the diodes show slight deterioration in rectifying behavior due to the onset of metallurgical reactions with the GaN. The experimental dependence of the reverse leakage current on bias and measurement temperature is inconsistent with both thermionic emission and thermionic field emission models, suggesting that leakage must originate from other mechanisms such as surface leakage or generation in the depletion layer through deep-level defects.

Single-phase GaGdN and GaGdN:Si films were grown on sapphire substrates by gas source molecular beam epitaxy using solid Gd, Ga, and Si sources and active nitrogen derived from a RF nitrogen plasma source. The undoped films were highly resistive films but became conductive with the addition of Si. Superconducting quantum interference device magnetometry indicated room-temperature ferromagnetism in both types of materials. Structural defects had a strong influence on the magnetic ordering of the material, as seen in a drastic reduction of magnetic moment with degrading crystalline quality. Magnetization of the codoped film increased with Si content, reaching levels higher than that of the undoped material. The Gd-doped AlN films grown in a similar fashion also displayed Curie temperatures above room temperature.

Single phase GaGdN and GaGdN:Si thin films were grown by gas source molecular beam epitaxy using solid Gd, Ga, and Si sources along with a RF nitrogen plasma. SQUID magnetometry indicated room temperature ferromagnetism in both materials. Defects played a large role in the magnetic ordering of the material, as seen in a drastic reduction of magnetic signal with degrading crystallinity. Highly resistive films became conductive with the addition of Si. Magnetization of the co-doped film increased with Si content, reaching levels higher than that of the singly-doped material.

In this paper, the authors report the nitride surface preparation and growth of these crystalline oxide dielectrics, efforts to improve the oxide/nitride interface properties by reducing the lattice mismatch and accelerated aging effects for these dielectrics on the nitride semiconductors. The authors review progress in obtaining low interface state densities and reducing current collapse with these dielectrics on GaN and examine the thermal stability and compatibility with processing schemes for HEMTs

A review is given of Ohmic and Schottky contacts to n- and p-type ZnO. It is relatively straightforward to form high-quality Ohmic contacts to n-type ZnO, with specific contacts resistivity in the range 10 −6 Ω cm 2 even for unnannealed contacts on strongly n-type layers, while recent work has also shown good results (10 −5 –10 −6 Ω cm 2 ) for Au or Ni/Au annealed at 300–600 °C. Schottky contacts to both n- and p-type ZnO are much lower than expected from the metal work function and the electron affinity of ZnO, suggesting that surface states are important in determining the effective barrier height. The Schottky contacts also show poor thermal stability. For transparent transistors based on ZnO, this suggests that oxide gates are more suitable than metal gates.

AlMnN and AlCrN have been synthesized by gas-source molecular beam epitaxy (GSMBE). Using optimized growth conditions and compositions, sccm films as determined by x-ray diffraction (XRD) and transmission electron microscopy, which also show room-temperature magnetic behavior were obtained for both materials. Chromium was found to produce greater magnetic ordering as evidenced by a higher technical saturation. The AlCrN also exhibited a higher remanent magnetization and a M versus T behavior more typical of ferromagnetism than that observed for AlMnN. These results suggest that Cr is a superior dopant for formation of AlN-based, dilute magnetic semiconductors.

Electrical and optical properties of p-AlGaN films grown by metalorganic chemical vapour deposition and implanted with high doses (3 × 1016 cm−2) of 250 keV Mn and Cr ions are reported. Schottky diodes prepared on such implanted films after annealing at 700 °C show a strongly increased reverse leakage current and increased series resistance in the forward direction due to residual radiation damage related defects. The density of these defects was considerably higher for the Mn-implanted diodes which correlated with the higher expected radiation damage due to higher ion mass of Mn compared with Cr. Deep level measurements revealed the formation of hole traps with levels near Ev + 0.4 eV and Ev + 1 eV. Optical absorption measurements indicated the presence of two major defect bands at about 1.5–1.7 eV and 2.25–2.35 eV. The results are compared with earlier measurements on Cr- and Mn-implanted p-GaN films and on proton-implanted p-AlGaN films.

Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external magnetic field (so-called “spin-LEDs”). The contact annealing temperature was kept to 750°C, which is the thermal stability limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and the n-GaN in the top contact layer.

Recent results on achieving ferromagnetism in transition-metal-doped GaN, A1N and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carrier ...

Recent results on achieving ferromagnetism in transition metal-doped GaN, SiC and related materials are discussed. While current generations of semiconductor electronic and photonic devices utilize the charge on electrons and holes in order to perform their specific functionality such as signal processing or light emission, the field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low power, high-speed memory, logic and photonic devices. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. Here we review the field of wide bandgap dilute magnetic semiconductors, such as GaN, SiC and related materials, exhibiting room temperature ferromagnetism, the origins of the magnetism and its potential applications.

Both ion implantation and epitaxial crystal growth provide convenient methods of introducing transition metals such as Mn,Cr,Fe,Ni and Co into GaN, GaP, SiC and ZnO for creating dilute magnetic semiconductors exhibiting room temperature ferromagnetism. In this paper we review progress in wide band gap ferromagnetic semiconductors and the role of defects and doping on the resulting magnetic properties.

Implantation of Mn or Cr at doses of 3–5 × 1016 cm−2 into Si-doped Al0.24Ga0.76P epilayers on GaP substrates produced ferromagnetic ordering at temperatures up to 300 K. The results were similar to those obtained previously in p-type AlGaP(C), indicating that both electron and hole-doped AlGaP can exhibit ferromagnetism. In addition, the AlGaP results are similar to those for GaP so the magnitude of the bandgap was not the main parameter influencing the Curie temperature, in contradiction to predictions from some mean-field theories. Second phases were not observed by X-ray diffraction and were not responsible for the ferromagnetism.

Electrical and luminescent properties of GaN/InGaN multiquantum well light emitting diodes (MQW LEDs) with the top p-GaN layer implanted with 3×10 16 cm −2 Mn ions for potential spin-polarized emission are reported. The forward current in the Mn-implanted diodes was limited by filling of hole traps in the high-resistivity implanted region, the most shallow hole traps having the activation energy of 0.27 eV. Admittance spectroscopy and deep level transient spectroscopy measurements also revealed the presence in the implanted region of traps with apparent activation energies of 0.23, 0.43, 0.5, 0.65 and 0.85 eV. Microcathodoluminescence spectra of the implanted diodes are dominated by two defect bands, the blue band centered near 2.8 eV and the yellow band centered near 2.25 eV, in contrast to the MCL spectra of the virgin diodes dominated by the 2.67 eV band coming from recombination in the GaN/InGaN MQW region. The high resistivity of the implanted region and the high density of deep traps in this region lead to a strong increase in the threshold voltage for the onset of electroluminescence from about 4 V before implantation to about 8 V after implantation.

Electrical and luminescent properties of normal p-side-up and inverted n-side-up light emitting diodes (p-LEDs and n-LEDs) and the effect of Mn incorporation into the upper n-type contact layer structure of GaN-based multiquantum-well MQW LEDs were studied. The latter structure is considered as promising for spintronic applications (spin-LED). It is shown that n-LEDs have more pronounced tunneling compared to p-LEDs and that the active region of the n-LEDs shows domain-like nonuniformities that are absent in p-LEDs. These nonuniformities seem to be related to local segregation of In in the GaN/InGaN MQWs and result in the emergency of double peaked electroluminescence (EL) spectra in n-LEDs. Introduction of Mn leads to strong increase of the resistivity of the GaMnN layer which gives rise to increased threshold voltage for observing the EL and decreased EL intensity.

Growth by molecular-beam epitaxy (MBE) of the dilute-magnetic alloy GaMnN is reported. The Mn concentration, as determined by Auger electron spectroscopy (AES), is found to be linear with increasing Mn-cell temperature up to ∼43at.%Mn. No second phases are observed for Mn levels below 9 at.%. The cubic-phase Mn4N is found to be the thermodynamically stable phase at the growth conditions used to produce GaMnN. Hysteresis in M versus H is observed in both GaMnN and GaMnN:C grown on both sapphire and metal-oxide chemical-vapor deposition (MOCVD) GaN at several growth temperatures. Magnetotransport results show the anomalous Hall effect, negative magnetoresistance, and magnetic hysteresis, indicating that Mn is incorporating into the GaN and forming the ferromagnetic-semiconductor GaMNN. Room-temperature hysteresis is obtained in magnetization measurements with an optimum Mn concentration of ∼3 at.%.

Existing semiconductor electronic and photonic devices use the charge on electrons and holes to perform their specific functionality, such as signal processing or light emission. The field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers, and integrated magnetic sensors. The use of such devices depends on the availability of materials with practical magnetic-ordering temperatures. Here, we summarize recent progress in the development of GaN and other wide bandgap semiconductors that retain ferromagnetic properties above room temperature.

Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

Results on the synthesis of ferromagnetic GaMnN and GaMnP by both Molecular Beam Epitaxy or implantation of Mn directly into p-GaN or GaP(C) at elevated temperatures to avoid amorphization will be described. There is a relatively broad range of growth conditions under which single-crystal, single-phase material may be obtained with significant Mn concentrations. The effects of background doping level are discussed, along with a comparison of results on direct implantation of Fe and Ni instead of Mn. Essential requirements for utilizing the spin of the electron in device structures include the ability to achieve efficient electrical spin injection and transport of spin-polarized carriers, along with effective detection of these carriers.

Optical absorption spectra, microcathodoluminescence (MCL) spectra, and electrical properties of GaMnN films grown by molecular-beam epitaxy with Mn concentration in the range of 3 to 10 at. % were studied. Optical absorption and MCL spectra show the presence of strong bands corresponding to the transition from the Mn acceptors near Ec−2 eV to the conduction band. The other strong band observed in MCL measurements was the blue band peaked near 2.9 eV and associated with the transition from the valence band to deep donors with a level near Ec−0.5 eV. All GaMnN samples were shown to be lightly n-type which suggests close self-compensation of the Mn acceptors by some native defect donors. A plausible scenario is that such compensating donors could be due to nitrogen vacancies and that the Ec−0.5 eV donor defects are complexes between the Mn acceptors and the nitrogen vacancy donors.

Optical transmission spectra, microcathodoluminescence spectra, capacitance–voltage and capacitance–frequency curves, temperature dependence of resistivity and deep level spectra with both electrical and optical injection were measured on n-GaN samples implanted with high doses of Mn (3×1016 and 4×1016 cm−2) and Co (4×1016 cm−2). From optical transmission it was found that Mn forms a deep acceptor near Ev+1.8 eV while the Co acceptor is about 0.1 eV deeper. In addition, Mn and Co form complexes with native defects and these complexes are deep electron traps with a level near Ec−0.5 eV. Such complexes are most likely responsible for a strong blue luminescence band with energy near 2.9 eV. Adjacent to the implanted region a defect region about 1 μm deep is formed, most likely by out-diffusion of point defects from the implanted zone during the 700 °C annealing used to partially remove the radiation damage. This region is characterized by a high density of electron traps at Ec−0.25 eV and Ec−0.7 eV and hole ...

GaN-based visible light-emitting diodes and laser diodes are already commercialized for a variety of lighting and data storage applications. This materials system is also showing promise for microwave and high power electronics intended for radar, satellite, wireless base stations, and utility grid applications; for biological detection systems; and for a new class of spin-transport electronics (spintronics) in which the spin of charge carriers is exploited. The explosive increase of interest in the AlGaInN family of materials in recent years has been fueled by the application of blue/green/UV light-emitting diodes (LEDs) in full-color displays, traffic lights, automotive lighting, and general room lighting (using so-called white LEDs) 1 . In addition, blue/green laser diodes can be used in high storage-capacity digital versatile disk (DVD) systems 2 . AlGaN-based photodetectors are also useful for solar-blind UV detection and have applications as flame sensors for control of gas turbines or detection of missiles.

The magnetization of p-GaN or p-AlGaN/GaN superlattices was measured after implantation with high doses (3–5×1016 cm−2) of Mn, Fe, or Ni and subsequent annealing at 700–1000 °C. The samples showed ferromagnetic contributions below temperatures ranging from 190–250 K for Mn to 45–185 K for Ni and 80–250 K for Fe. The use of superlattices to enhance the hole concentration did not produce any change in ferromagnetic ordering temperature. No secondary phase formation was observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis for the doses we employed.

Cr concentrations of ∼2at.% were incorporated into AlN during growth by molecular beam epitaxy. Under optimized conditions, single-phase, insulating AlCrN is produced whose band gap shows a small (0.1–0.2eV) decrease from the value for undoped AlN (6.2eV), a decrease in a-plane lattice constant and the introduction of two absorption bands at 3 and 5eV into the band gap. This material shows ferromagnetism with a Curie temperature above 300K as judged from the difference in field-cooled and zero-field-cooled magnetization. For nonoptimized growth, second phases of Cr2N and AlxCry are produced in the AlN and the material is conducting (∼1000Ωcm) with activation energy for conduction of 0.19eV and apparent band gap of 5.8eV.

The effects of nucleation layer and growth temperature on the magnetic properties of GaMnN have been investigated. It was found that the largest magnetic moment was measured in films prepared on metalorganic chemical vapor deposition (MOCVD) GaN buffers at a growth temperature of 700 °C. Extended x ray absorption fine structure measurements indicate that the improved magnetic quality of the films grown on MOCVD layers versus gas source molecular beam epitaxy nucleation layers is not due to a change in the lattice position of the Mn and is more likely due to a reduction in defect density. Growth temperature was also found to have a significant impact on the magnetic properties, with the optimal growth temperature found to be 700 °C.

Spin polarization of GaMnN/InGaN light-emitting diodes grown by molecular beam epitaxy is analyzed. In spite of the ferromagnetic behavior of the GaMnN spin injector, the diodes are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN spin detector, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection.

The room temperature magnetization of GaMnN films grown by molecular beam epitaxy on (0001) sapphire substrates with Mn concentrations varying from 0 to 9 at. % was found to depend on Mn concentration, with a maximum magnetization found at ∼3 at. % Mn. High-resolution x-ray diffraction measurements show that the c-plane lattice constant initially decreases with increasing Mn concentration, then increases when the Mn content increases above ∼3 at. %. This increase is accompanied by a decrease in the full width at half maximum of the rocking curves. Extended x-ray absorption fine structure results indicate that the nonsubstitutional Mn is not present in the form of GaxMny clusters and thus is most likely present in the form of an interstitial. Optical absorption measurements show only a slight increase in the band gap for material with 3 at. % Mn, relative to undoped GaN.

Single-phase (Ga,Mn)N layers grown by molecular beam epitaxy with ∼3 at. % Mn were exposed to 2H or 1H plasmas under conditions designed to permeate layers with hydrogen. No evidence of the formation of Mn–H complexes could be detected from either infrared spectroscopy or the changes in magnetic properties. However, the residual magnetization increased ∼20% after hydrogenation, consistent with passivation of crystal defects in (Ga,Mn)N. Hydrogenation may be an attractive method for improving the magnetic properties of these heteroepitaxial materials.

AlN films grown by gas-source molecular beam epitaxy were doped with different levels of Mn during growth. High resolution x-ray diffraction characterization revealed good crystallinity in single phase material, with lattice constant decreasing with increasing Mn concentration. Single phase AlMnN was found to be p type while AlMnN/AlMn mixed phase material was found to be highly conductive n type. Magnetization measurements performed with a superconducting quantum interference device magnetometer indicated ferromagnetism in single phase material persisting to 300 K and showed no evidence of room temperature magnetization in multiphase material. In particular, it was shown that Mn4N second phases are not contributing to the magnetization in the AlMnN under optimized growth conditions.

We report temperature-dependent optical spectra of ferromagnetic Mn-doped GaN in a wide photon energy region of 5 meV–4 eV. Below the GaN gap, an absorption peak around 1.25 eV whose intensity increases at lower temperatures was observed. A composite medium theory, called the Maxwell–Garnett theory, shows that the absorption peak can be assigned to a sphere resonance from metallic particles embedded in a Mn-doped GaN matrix. We also report that the far-infrared absorption of Mn-doped GaN sample was very small. This result suggests that itinerant carrier-mediated ferromagnetism does not fully explain the observed magnetic properties.

Ion implantation of Mn or Cr at concentrations of 1–5 at. % were performed in AlxGa1−xP (x=0.24,0.38) epilayers grown by gas source molecular beam epitaxy. Ferromagnetic-like ordering above 100 K for Cr and 300 K for Mn was observed in superconducting quantum interference device measurements. Structural characterization revealed no second phases that could influence the measured magnetic properties. As the AIP mole fraction in the AlxGa1−xP layers increased, the magnetic ordering temperatures were generally observed to increase, while the calculated magnetic moment decreased. Mn appears to be a more promising choice than Cr for high temperature ferromagnetism in AlGaP.

Lateral electron mobilities in 0.2-μm-thick n-(Ga, Mn)N films were obtained from Hall measurements, producing values of 116∼102 cm2/V s in the temperature range from 298 to 373 K. These values are comparable to, but slightly lower than, electron mobilities in n-GaN of the same electron concentration. By sharp contrast, analysis of the reverse saturation current in mesa Schottky diodes fabricated in the n-(Ga, Mn)N show vertical electron mobilities of 840∼336 cm2/V s in the temperature range from 298 to 373 K. This is consistent with a reduction in electron scattering by charged dislocations for vertical transport geometries [M. Misra, A. V. Sampath, and T. D. Moustakas, Appl. Phys. Lett. 76, 1045 (2000)].

The Schottky barrier height of Pt contacts on n-(Ga,Mn)N (n∼3.5×1017 cm−3) thin films was obtained from current–voltage measurements as a function of temperature. The resulting values ranged from 0.82±0.04 eV at 25 °C to 0.79±0.06 eV at 100 °C with saturation current densities of 4.28×10−8 A cm−2 (25 °C) to 8.42×10−5 A cm−2 (100 °C), respectively. The barrier height at room temperature obtained from an activation energy plot was 0.91±0.06 eV. The reverse current magnitude was larger than predicted by thermionic emission alone, just as in n-GaN grown in a similar fashion on Al2O3 substrates. The measured barrier height for Pt on n-(Ga,Mn)N is lower than for the value reported on n-GaN(1.08 eV).

GaMnN thin films were synthesized using gas-source molecular-beam epitaxy. Mn concentrations between 3 and 12 at. % were investigated. No evidence of second-phase formation was observed by powder x-ray diffraction or high-resolution cross section transmission electron microscopy in films with 9% or less Mn. The films were n type as determined by capacitance–voltage or Hall analysis. Magnetic characterization performed using a squid magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Mn showed the highest degree of ordering per Mn atom. At 320 K, the samples show a nonzero magnetization indicating a TC above room temperature.

GaN and AlN thin films were implanted with gadolinium (Gd)atoms and characterized using deep ultra-violet (UV) photoluminescence(PL). The Gd-implanted samples were annealed at temperatures up to 1178K in a flowing N2 gas to facilitate recovery of implantation-related damage. Using the output at 195 nm from a quadrupled Ti:sapphire laser, narrow PL emission was observed at 318 nm from the Gd- implanted AlN thin films. This emission is characteristic of the lowest energy 4f transition of the trivalent Gd ion. A boarder emission band, also centered at 318 nm, was observed under excitation at 266 nm. No PL emission was observed from the Gd-implanted GaN thin films at either the bandedge or due to a 4f transition. The dependence of the UV emission on AlN sample temperature was systematically studied. The peak PL emission intensity decreased by less that a factor of 3 over the temperature range of 10 K to 300 K. Decay transients of the UV emission were measured indicating that the lifetime of this emission is very fast.

Single phase GaGdN and GaGdN:Si films were grown on sapphire substrates. The undoped films were highly resistive films but became conductive with the addition of Si. SQUID magnetometry indicated room temperature ferromagnetism in both types of materials. Structural defects had a strong influence on the magnetic ordering of the material, as seen in a drastic reduction of magnetic moment with degrading crystalline quality. Magnetization of the co-doped film increased with Si content, reaching levels higher than that of the undoped material. Gd-doped AlN films grown in a similar fashion also displayed Curie temperatures above room temperature.

Electrical and optical spin injection efficiency of GaMnN/InGaN spin LEDs is evaluated. At room temperature, the spin LEDs are shown to exhibit negligible optical and electrical spin injection efficiency despite that the n‐type GaMnN spin injector employed is ferromagnetic. On the other hand, carrier supply from GaMnN at low temperatures is accompanied by a reduction (by 1–5%) in optical polarization of the InGaN spin detector (SD) from its intrinsic values measured without carrier supply from GaMnN. This observation seems to indicate some degrees of spin injection from GaMnN with the spin orientation opposite to that of the lowest spin state of the SD. The very low degree of polarization, however, implies efficient spin loss during the spin injection process. From cw‐ and transient resonant optical orientation studies, the spin loss is attributed to fast spin relaxation within the InGaN spin detector.

Theoretical and experimental studies of GaMnN/GaN/InGaN structure for a spin LED device were performed. Strong electron spin relaxation was experimentally observed in a InGaN/GaN quantum well. It is shown that the strong spin relaxation might result from the built‐in piezoelectric field in strained wurzite heterostructures. A five level k ⋅ p model was used for microscopic calculations of the structure inversion asymmetry induced spin‐orbit interaction. The magnitude of this interaction is shown to be comparable with that in InGaAs/GaAs quantum structures.

The aim of this chapter is to discuss ferromagnetism in gallium nitride (GaN) and related materials. This chapter elucidates recent results on achieving ferromagnetism in transition metal-doped GaN, AlN, and related materials. While current generations of semiconductor electronic and photonic devices utilize the charge on electrons and holes to perform their specific functionality such as signal processing or light emission, the field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers, and integrated magnetic sensors. There is strong potential for new classes of ultralow power, high-speed memory, logic, and photonic devices. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. This chapter discusses the current state-of-the-art in producing ferromagnetism in GaN and related materials, exhibiting room temperature ferromagnetism, the origins of the magnetism, and its potential applications.

Epitaxial growth of the ferromagnetic semiconductors GaMnP:C and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP:C films grown with 9.4% Mn are found to be p-type with hysteretic behavior to room temperature. GaMnN films grown at 700 °C with 2.8% Mn show hysteresis at 300 K, while temperature-dependent magnetization measurements indicate that the magnetism may persist to much higher temperatures (> 325 K). Samples of AlGaMnN have also been prepared for the first time that show improved surface morphology compared to GaMnN but which show only paramagnetic behavior.

GaGdN and GaCrN films grown by gas source molecular beam epitaxy were irradiated with high energy (10 and 40?MeV) protons at a fluence of 5 ? 109?cm?2 to examine the effect on magnetization. This dose is equivalent to the exposure expected in 10 years in low-earth orbit space missions. Both photoluminescence intensity and magnetization of the films showed significant decreases with irradiation. The largest response was observed with GaGdN, which experienced a 50?60% loss in band edge luminescence and 11?83% loss in magnetic saturation. After annealing the irradiated samples at 500?? C under a nitrogen plasma ambient, both types of films experienced a complete recovery in magnetic properties. The fact that the introduction of point defects did not increase the magnetization is evidence against unpaired bonds from defects in the film being responsible for the magnetic properties in the films.

Deep ultraviolet emission from gadolinium (Gd)-implanted AlN thin films has been observed using photoluminescence (PL) spectroscopy. The AlN epilayers were ion implanted with Gd to a total dose of similar to 6x10(14) cm(-2). Using the output at 197 nm from a quadrupled Ti:sapphire laser, narrow PL emission was observed at 318 nm, characteristic of the trivalent Gd ion. A broader emission band, also centered at 318 nm, was measured with excitation at 263 nm. The PL emission intensity decreased by less than a factor of 3 over the sample temperature range of 10-300 K and decay transients were of the order of nanoseconds.

GaN films were doped with Eu to a concentration of ∼0.12at.% during growth at 800°C by molecular beam epitaxy, with the Eu cell temperature held constant at 470°C. All samples were postannealed at 675°C. The films exhibited strong photoluminescence (PL) in the red (622nm) whose absolute intensity was a function of the Ga flux during growth, which ranged from 3.0×10−7to5.4×10−7Torr. The maximum PL intensity was obtained at a Ga flux of 3.6×10−7Torr. The samples showed room temperature ferromagnetism with saturation magnetization of ∼0.1–0.45emu∕cm3, consistent with past reports where the Eu was found to be predominantly occupying substitutional Ga sites. There was an inverse correlation between the PL intensity and the saturation magnetization in the films. X-ray diffraction showed the presence of EuGa phases under all the growth conditions but these cannot account for the observed magnetic properties.

GaGdN layers were grown by gas source molecular beam epitaxy with varying crystal quality and Gd concentrations as set by the Gd cell temperature. Magnetic measurements showed ferromagnetic behavior at room temperature, with the saturation magnetization dependent both on Gd concentration and crystalline quality. The Gd concentration was under the detection limit of secondary ion mass spectrometry, and estimated to be on the order of

Gd+ ions were implanted at total doses of 3-6x10(14) cm(2) into single-crystal GaN or AlN epilayers grown on sapphire substrates and annealed at 700-1000 degrees C. The implanted Gd showed no detectable diffusion in either material after annealing, as measured by secondary ion mass spectrometry, corresponding to a diffusion coefficient < 8x10(-12) cm(2) s(-1). Under all annealing conditions, x-ray diffraction shows the formation of second phases. In the case of GaN, these include Gd3Ga2, GdN, and Gd, while for AlN only Gd peaks are observed. Both the GaN and AlN show high saturation magnetization after annealing at 900 degrees C (similar to 15 emu cm(-3) for GaN and similar to 35 emu cm(-3) for AlN). The magnetization versus temperature characteristics of the Gd-implanted GaN show a blocking behavior consistent with the presence of precipitates, whereas the AlN shows a clear difference in field-cooled and zero-field-cooled magnetization to above room temperature which may also be due to Gd inclusions. (c) 2006 American Institute of Physics

Transient magneto-optical spectroscopy of InGaNGaN and InGaNGaMnN quantum wells reveals a spin relaxation process with a characteristic time of 50 ps. We show that the observed spin relaxation is m ...

saturation current in HENTs had increases of 4.5% and 1%, respectively, for Mg0.5Ca0.5O and Mg0.25Ca0.75O passivated devices. However, there was a 10% decrease for the device passivated with pure MgO. This was due to strain applied on the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride form the lattice mismatch between AlGaN and GaN. From pulsed measurements, HEMTs passivated with Mg0.5Ca0.5O and Mg0.25Ca0.75O showed higher passivation effectiveness 90% of dc current then the MgO passivated HEMTs 83% dc current. This is due to the closer lattice matching of these calcium containing oxides and the reduction in interface traps associated with lattice mismatch. © 2005 American Institute of Physics. DOI: 10.1063/1.2105987

GaCrN thin films were synthesized using gas-source molecular beam epitaxy. No evidence of second-phase formation was observed by powder x-ray diffraction. Magnetic characterization performed using a superconducting quantum interference device magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Cr showed the highest degree of ordering. No evidence of segregation was found from secondary ion mass spectroscopy analysis. The oxygen content of the film was found to be ∼1019cm−3. After rapid thermal annealing at temperatures up to 700 °C in a nitrogen ambient for 1 min, the room temperature saturation magnetization of the GaCrN films remained virtually unchanged, in contrast to similarly prepared GaMnN films.