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The stimulated emissions from semipolar InGaN laser diode (LD) structures grown on (112¯2) GaN substrates are observed at room temperature under photopumped conditions. The measured emission peaks are in the photon energy range from 2.62eV (474nm)to3.05eV (405nm), and the emission intensity has a threshold behavior with respect to the pumping power. A strong in-plane optical anisotropy is observed between the two perpendicular directions, [1¯1¯23] and [11¯00], due to anisotropic matrix elements, which depend on the crystal orientation; the stimulated emission measured along the [1¯1¯23] direction occurs with a lower threshold pumping power at a lower energy compared to that obtained along the [11¯00] direction. The experimental results and the valence band calculations indicate that the transverse-electric mode with an electric vector along the [11¯00] direction is dominant for gain formation in semipolar and nonpolar InGaN LDs. Compared to c-plane InGaN LDs, semipolar InGaN LDs have comparable or less th...

The authors measure the interplay of piezoelectric field and built-in potential on carrier recombination and quantum confined Stark effect in green light emitting InGaN quantum wells by modulating the external bias voltage of the pn junction. Time-resolved electroluminescence shows a temporal separation of carrier injection into the active region and radiative recombination within the InGaN quantum wells. During the time when the bias voltage is off, the piezoelectric field is partially compensated by the built-in potential of the pn junction, resulting in an increased radiative recombination rate.

Nanoscopic optical characterization using scanning near field optical microscopy was performed on a (112¯2) microfacet quantum well (QW). It was revealed that the carrier diffusion length in the (112¯2) QW is less than the probing fiber aperture of 160nm, which is shorter than that of the (0001) QWs and is attributed to much faster radiative recombination processes in the (112¯2) QW due to a reduced internal electric field. Owing to this short diffusion length, the correlation between the internal quantum efficiency (IQE) and emission wavelength is elucidated. The highest IQE is ∼50% at 520nm, which is about 50nm longer than in (0001) QWs, suggesting that the (112¯2) QW is a suitable green emitter.

Basal-plane slip has been observed in InGaN∕GaN heterostructures containing a high density of threading dislocations. The InGaN epilayers were deposited on a GaN mesa structure grown by metal-organic chemical vapor deposition on (0001) sapphire substrates using conventional methods. The glide process starts at the edge of the mesas, generating misfit dislocation half loops with a Burger vector of 1∕3⟨112¯0⟩. The misfit dislocation propagation is shown to depend on the crystalline orientation of the mesa edge and results in relaxation of over 80% of the misfit strain. Pinning of the misfit dislocation loops by threading dislocations does not stop them from propagating into the layer. No reaction is observed between the dislocation loops and the threading dislocations. The number of dislocation loops and their propagation distance increase with the indium content of the InGaN epilayers, indicating that the process is driven by the misfit strain. As a result of plastic relaxation, InGaN epilayers are observe...

Optical gain spectra presented for (Al,In)GaN laser diodes with lasing wavelength ranging from UV (375 nm) to aquamarine (470 nm) show a strong increase in inhomogeneous broadening, caused by Indium composition and quantum well width fluctuations which increase with Indium mole fraction. These gain spectra provides a standard data set for the calibration of microscopic many-body simulations. We demonstrate by comparison with basic simulations that the different assumptions of a global constant carrier density or of global constant quasi-Fermi levels for electrons and holes lead to a strikingly different dependency of optical gain on carrier density. For constant quasi-Fermi levels the threshold carrier density becomes insensitive to inhomogeneous broadening for realistic parameters. This is in agreement with the observation that the threshold current is nearly independent over the wavelength range from near UV to aquamarine.

— We succeeded in fabricating high-output-power blue (445 nm) laser diodes (LDs) with an output power of 500 mW. The operating current, voltage, and wall-plug efficiency of these LDs were 480 mA, 4.8 V, and 21.7%, respectively. The lifetime of these LDs was estimated to be 10,000 hours under continuous-wave operation at 25°C. From examination of the degradation mode, we found that the operating current seriously affects the lifetime of LDs. In the next stage, we will focuse on the optimization and sophistication of the manufacturing processes to fabricate longer-lifetime (>30,000 hours) blue LDs.

Optical gain spectra were measured for InGaN-based laser diodes (LDs) emitting at 406nm (LD406) and 470nm (LD470) by employing the Hakki-Paoli method. The internal loss coefficient was as large as 35cm−1 for the LD470 compared to 25cm−1 for LD406. Moreover, gain saturation was observed at about 490nm just below the lasing threshold, and a gain band appears at higher photon energies for further carrier injection resulting in lasing at 470nm. Spontaneous emission peaks of electroluminescence were measured as a function of injection current density below threshold for both samples. The authors attribute the huge blueshift of the spontaneous emission of LD470 up to 450meV to a filling of the localized tail states in addition to that caused by the screening of the piezoelectric field. The blueshift for the LD406 was as small as about 30meV and can be interpreted as a result of the screening by both injected carriers and dopants.

InGaN quantum wells grown in the conventional [0001] direction are known to exhibit long carrier lifetimes that are attributed to strong internal electric fields due to spontaneous and piezoelectric polarization. These fields are expected to be considerably reduced in other crystal geometries. In this work, the authors have investigated the carrier dynamics of InGaN single quantum wells grown parallel to {112¯2} planes. The carrier lifetimes, measured by time-resolved cathodoluminescence, are considerably smaller than for quantum wells grown in the conventional c-plane geometry. In addition, the lifetime does not change significantly with varying indium composition or increasing well width. Electron holography measurements of the electrostatic potential across these quantum wells confirm that the internal fields in this geometry are negligible. These results are of interest for the development of higher-efficiency light-emitting diodes using alternative substrate orientations.

GaN and InGaN∕GaN multiple quantum well (MQW) were grown on semipolar (112¯2) GaN bulk substrates by metal organic vapor phase epitaxy. The GaN homoepitaxial layer has an atomically flat surface. Optical reflection measurements reveal polarization anisotropy for the A, B, and C excitons. Free A excitons dominate the photoluminescence (PL) spectrum at 10K and are accompanied by a weaker, sharp doublet emission due to neutral donor-bound excitons. The InGaN∕GaN MQW grown on a GaN homoepitaxial layer involves fast radiative recombination processes. The PL decay monitored at 428nm can be fitted with a double exponential curve, which has lifetimes of 46 and 142ps at 10K. These values are two orders of magnitude shorter than those in conventional c-oriented QWs and are attributed to the weakened internal electric field. The emissions from GaN and MQW polarize along the [11¯00] direction with polarization degrees of 0.46 and 0.69, respectively, due to the low crystal symmetry.

The authors have observed that for InxGa1−xN epitaxial layers grown on bulk GaN substrates exhibit slip on the basal plane, when in the presence of free surfaces that intercept the heterointerface and for indium compositions x⩾0.07. This leads to almost complete relaxation of the local misfit strain by generation of radial-shape dislocation half loops. For x⩾0.17, generation of straight misfit dislocations by glide on the secondary ⟨112¯3⟩ {112¯2} slip system is observed, in addition to the radial-shape half loops at surface pits. These two mechanisms act independently with no observed interaction between them, leading to the conclusion that slip on the basal plane occurs first during the growth process. The secondary slip system is activated later and involves a significantly higher critical stress energy.

We derive the equation for the internal quantum efficiency (IQE) and its temperature dependence of luminescence. In general, time-resolved photoluminescence (TRPL) must be carried out by changing temperature to obtain the efficiency and the dependence; however, they can be obtained by fitting the equation derived in this study to the temperature characteristics of luminescence integrated intensity. Thus, they are obtained without carrying out TRPL experiments. The equation is applicable to the characteristics not restricted by the measurement method. It is also applied to any semiconductor whose luminescence integrated intensity decreases with increasing temperature. In this study, the equation is applied to the luminescence characteristics of In x Ga1-x N/GaN multiple quantum wells. These luminescence characteristics are analyzed in terms of the IQE and the temperature dependence derived using the equation and interpreted in connection with In composition fluctuations, strain effects, and interface quality.

A color synthesis based on InGaN∕GaN quantum wells (QWs) grown on GaN microfacets formed by regrowth on SiO2 mask stripes is demonstrated. The microfacet structure is composed of (0001), {112¯2}, and {112¯0} planes, and the InGaN well thickness and composition are spatially inhomogeneous due to the diffusion of the adatoms among the facets. These properties allow microfacet QWs, which, for example, emit yellow from the (0001) facet and blue from the {112¯2} facet, to be fabricated, of which the luminescence appears white due to the additive color mixing. Using a mask pattern that consists of regions with and without stripes, the emissions from the microfacet QWs and from planar QWs are synthesized to produce the desired apparent output colors.

We report on the presence of optically active stacking faults on basal and prismatic planes in epitaxially laterally overgrown GaN (ELOG) on {112¯2} facets. The structure of the faults has been analyzed using diffraction contrast electron microscopy. We show that stacking faults on {112¯0} prismatic planes involve a lattice displacement of 12⟨11¯01⟩, parallel to the fault plane. They appear as jogs connecting basal-plane stacking faults, the latter with a lattice displacement of 16⟨202¯3⟩. These faults are observed only in the laterally overgrown regions that grow on {112¯2} planes, which indicates that the stacking fault formation is closely related to the orientation of the growth surface. Possible formation mechanisms of these faults are discussed. Direct correlation between TEM and cathodoluminescence shows that these prismatic-plane and basal-plane stacking faults are optically active with light emission at 3.30 and 3.41eV, respectively.

We investigate a peculiar optical instability (blinking) phenomena associated with spatial inhomogeneity in InxGa(1−x)N single quantum well systems. We studied the time dependence of this dynamic phenomenon and tested a “quantum jump” single exponential model on the system. A comparative analysis of the behavior of different samples suggests that indium-rich localized centers participate in the mechanism of blinking and that the instability behavior differs with the excitation wavelength. Our study indicates that the trapping and de-trapping process between the localized-luminescent centers and surrounding less luminous regions plays important roles in the carrier recombination mechanism.

We succeeded fabricating high power blue (445nm) laser diodes (LDs) with an output power of 500mW. The operating current, voltage and wall-plug efficiency of these LDs were 480mA, 4.8V, and 21.7%, respectively. Estimated Lifetime of these LDs was over 10,000h under continuous-wave operation at 25 °C.

Rainbow color luminescence from InxGa1−xN single quantum wells (SQWs) is achieved and almost covers the entire visible range when the layers are fabricated on {112¯2} facets with a few micron-width using a regrowth technique on striped GaN templates. These facets are tilted 56° with respect to the (0001) facets and border the (0001) and {112¯0} facets. The emission wavelength on the {112¯2} facets is redshifted from the {112¯0} side to (0001) side due to the variations of the In composition, which leads to the color contrast with the rainbow geometry. The temperature dependence of the photoluminescence intensity shows that the internal quantum efficiency at room temperature is 33% due to the very small internal electric fields and a small threading dislocation density compared to that in conventional (0001) InxGa1−xN SQWs. Since the emission efficiency does not show a noticeable emission wavelength dependence, this type of structure has potential as light-emitting devices with multiwavelengths that perfor...

We have studied the properties of InGaN∕GaN quantum wells grown on epitaxially laterally overgrown GaN stripes. The stripes have a triangular cross section due to {112¯2} crystalline facets. We have observed that the integrated light emission from such structures is uniformly polychromatic over a wide range of the visible spectrum. Using cathodoluminescence techniques, we find that the local emission wavelength increases steadily along the facets, in the direction away from the substrate. The gradient in the emission wavelength is related to the dependence of the quantum well width on the relative position along the facet. The continuous variation of the quantum well properties causes a uniform, polychromatic luminescence band. For some conditions, such distribution can resemble solar-white light emission. This approach can be used to produce an integrated white light source for monolithically integrated white light-emitting diodes.

We have found for the first time that blue emission from Mg-doped GaN was greatly enhanced by remote plasma treatment (RPT) with plasma containing atomic hydrogen, in particular, water vapor plasma, at low temperatures of 300–400°C. The highest enhancing factor was twenty, achieved by water vapor RPT at 400°C for 30 min. The enhanced blue emission was stable up to 500°C, similarly to blue emission from as-grown samples, suggesting the same origin and mechanism. We have confirmed that the emission mechanism is donor–acceptor pair (DAP) recombination, and have concluded that RPT produces a hydrogen-related donor level at E c-0.37 eV involved in the DAP emission.

We have developed high power blue laser diodes (LDs) with an emission wavelength of 445 nm by using GaN material. The operating current and voltage of these LDs at an output power of 200mW were 274 mA and 4.9 V, respectively. The estimated lifetime was over 10,000h under 25 °C continuous-wave operation at an output power of 200 mW.

Ultraviolet (UV) light-emitting diode (LED) epilayers were grown on low dislocation density (1×108/cm2) GaN templates with sapphire substrates. Then, the GaN templates and sapphire substrates were removed using laser-induced lift-off and polishing techniques. Additionally, to enhance the extraction efficiency, this LED chip used a higher reflectance Ag p-type electrode, patterned surface, and silicone resin molding package. When this UV LED was operated at a forward-bias pulsed current of 1 A at room temperature, the peak wavelength, output power, forward voltage, and external quantum efficiency were 365 nm, 1.5 W, 4.4 V, and 44%, respectively.

Ultraviolet (UV) laser diodes (LDs) whose active layers were composed of quaternary Al x In y Ga(1-x-y)N were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We investigated the Al and In mole fractions dependence of LD characteristics in the UV region. The emission wavelength of the LDs whose active layers consisted of Al0.03In0.02Ga0.95N single quantum well (SQW) was 366.4 nm under pulsed current injection at room temperature. The lasing wavelength was the shortest ever reported for III-V nitride-based LDs. The Al0.03In0.03Ga0.94N SQW UV LDs were demonstrated under 25°C continuous-wave (cw) operation. The threshold current density and voltage of these LDs were 3.5 kA/cm2 and 4.8 V, respectively. The estimated lifetime was approximately 500 h under 25°C cw operation at an output power of 2 mW.

The ultraviolet laser diodes (LDs) whose active layers consisted of binary GaN were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. For the first time, we observed the lasing emission from binary GaN active layer by current injection. The emission wavelength of GaN single quantum well LDs was 366.9 nm under pulsed current injection and 369.0 nm under continuos-wave (cw) operation at room temperature. The threshold current density and voltage of these LDs under the 25°C cw operation were 3.5 kA/cm2 and 4.6 V, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.

InGaN multi-quantum-well-structure laser diodes (LDs) with an emission wavelength of longer than 420 nm were grown on both an epitaxially laterally overgrown GaN (ELOG) substrate and an ELOG on a free-standing GaN substrate by a metaorganic chemical vapor deposition method. The wavelength dependence of InGaN LD characteristics was investigated. It was found that there was a strong relationship between the threshold current density and the emission wavelength of LDs. The LDs with the emission wavelength of 450 nm grown on the ELOG on a free-standing GaN substrate were demonstrated. The threshold current density and voltage of these LDs were 2.8 kA/cm2 and 4.5 V, respectively. The estimated lifetime was approximately 5000 h under 50°C continuous-wave operation at an output power of 5 mW.

Frequency (ω) dependent conductance (G) has been measured of the reverse-biased blue and green light-emitting diodes consisting of nitride semiconductors, in order to study the electronic behavior of the Mg acceptor in metalorganic chemical vapor deposition grown p-Al0.2Ga0.8N. Four peaks with activation energies of 14, 63, 115, and 166 meV were found in the G/ω vs ω characteristics of the diodes. Although these activation energies do not correspond directly to the energy depths above the valence band edge, it is likely that they reflect the complex electronic structure of the Mg acceptor levels.

An InGaN multiple-quantum-well laser diode wafer that lased at around 400 nm was shown to have the InN mole fraction, x, of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift (SS) of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E0, was estimated to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells was estimated to be as small as 300 kV/cm, SS was considered to originate from effective band-gap inhomogeneity. Because the well thickness fluctuation was insufficient to reproduce SS or E0 and bulk cubic In0.02Ga0.98N that does not suffer any polarization field or thickness fluctuation effect exhibited a SS of 140 meV at 77 K, the exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clusteri...

Ultraviolet (UV) InGaN and GaN single-quantum-well-structure light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. When the emission wavelength of UV InGaN LEDs was shorter than 380 nm, the external quantum efficiency (EQE) of the LED on ELOG was much higher than that on sapphire only under high-current operation. At low-current operation, both LEDs had the same EQE. When the active layer was GaN, EQE of the LED on sapphire was much lower than that on ELOG even under low-and high-current operations, due to the lack of localized energy states formed by alloy composition fluctuations. When the emission wavelengths were in the blue and green regions, EQE was almost the same between LEDs on both ELOG and sapphire due to a large number of deep localized energy states formed by large alloy composition fluctuations. The localized energy states are responsible for the high efficiency of InGaN-based LEDs in spite of a large number of dislocations.

Highly efficient light-emitting diodes (LEDs) emitting ultraviolet (UV), blue, green, amber and red light have been obtained through the use of InGaN active layers instead of GaN active layers. Red LEDs with an emission wavelength of 675 nm, whose emission energy was almost equal to the band-gap energy of InN, were fabricated. The dependence of the emission wavelength of the red LED on the current (blue shift) is dominated by both the band-filling effect of the localized energy states and the screening effect of the piezoelectric field. In the red LEDs, a phase separation of the InGaN layer was clearly observed in the emission spectra, in which blue and red emission peaks appeared. In terms of the temperature dependence of the LEDs, InGaN LEDs are superior to the conventional red and amber LEDs due to a large band offset between the active and cladding layers. The localized energy states caused by In composition fluctuation in the InGaN active layer contribute to the high efficiency of the InGaN-based emitting devices, in spite of the large number of threading dislocations and a large effect of the piezoelectric field. The blue and green InGaN-based LEDs had the highest external quantum efficiencies of 18% and 20% at low currents of 0.6 mA and 0.1 mA, respectively.

A violet InGaN multi-quantum-well (MQW)/GaN/AlGaN separate-confinement-heterostructure laser diode (LD) was grown on epitaxially laterally overgrown GaN on sapphire. The threshold current density was 3.9 kA/cm2. The LDs with cleaved mirror facets showed an output power as high as 30 mW under room-temperature continuous-wave (CW) operation. The stable fundamental transverse mode in the near-field patterns was observed at an output power up to 30 mW. The lifetime of the LDs at a constant output power of 5 mW was more than 1,000 h under CW operation at an ambient temperature of 50°C. The estimated lifetime was approximately 3,000 h under these high-power and high-temperature operating conditions.

Current and temperature dependences of the electroluminescence of InGaN UV/blue/green single-quantum-well (SQW)-structure light-emitting diodes (LEDs) were studied. The emission mechanism of InGaN SQW-structure LEDs with emission peak wavelengths longer than 375 nm is dominated by carrier recombination at large localized energy states caused by In composition fluctuation in the InGaN well layer. When the emission peak wavelength becomes shorter than 375 nm, the conventional band-to-band emission mechanism becomes dominant due to poor carrier localization resulting from small In composition fluctuations. In addition, the quantum-confined Stark effect due to the piezoelectric field becomes dominant, which causes a low output power of the UV LEDs.

InGaN single-quantum-well-structure blue light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The emission spectra showed the similar blue shift with increasing forward currents for both LEDs. The output power of both LEDs was almost the same, as high as 6 mW at a current of 20 mA. The LED on sapphire had a considerable amount of leakage current in comparison with that on ELOG. These results indicate that the In composition fluctuation is not caused by dislocations, the dislocations do not act as nonradiative recombination centers in the InGaN, and the dislocations forms the leakage current pathway in InGaN.

High-efficiency amber InGaN single-quantum-well (SQW) structure light-emitting diodes (LEDs) with a luminous efficiency of 10 lm/W were developed. At a current of 20 mA, the external quantum efficiency, the output power and the emission wavelength of the amber InGaN SQW structure LEDs were 3.3%, 1.4 mW and 594 nm, respectively. The output power of InGaN LEDs was about twice as high as that of AlInGaP LEDs. There was a large difference in the temperature dependence of the output power between InGaN and AlInGaP LEDs. When the ambient temperature was increased from room temperature to 80°C, the output power of AlInGaP LEDs decreased dramatically. On the other hand, the output power of the InGaN LEDs remained almost constant.

P-GaN/n-InGaN/n-GaN double-heterostructure (DH) blue-light-emitting diodes (LEDs) were fabricated successfully for the first time. The output power was 125 µW and the external quantum efficiency was as high as 0.22% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half-maximum (FWHM) of the electroluminescence (EL) were 440 nm and 180 meV, respectively. This value FWHM of was the smallest ever reported for blue GaN LEDs.

InGaN films were grown on GaN films with a high indium source flow rate and high growth temperatures between 780°C and 830°C. Strong and sharp band-edge (BE) emissions between 400 nm and 445 nm were observed, while deep-level emissions were barely observed in photoluminescence (PL) measurements at room temperature. The full width at half-maximum (FWHM) of the BE emissions was about 70 meV. The FWHM of the double-crystal X-ray rocking curve (XRC) from the InGaN films was about 8 minutes. This value of FWHM was the smallest one ever reported for InGaN films, and was almost the same as that of the GaN films which were used as the substrate.

Si- and Ge-doped GaN films were grown with GaN buffer layers. Si-doped GaN films, of which the carrier concentration was as high as 2×1019/cm3, were obtained. Every Si-doped GaN film showed a surface morphology that was smooth and mirrorlike. Ge-doped GaN films, of which the carrier concentration was as high as 1×1019/cm3, were obtained. Surface morphology of Ge-doped GaN films became poor around this carrier concentration. Both dopings showed good linearity of the carrier concentration as a function of the flow rate of GeH4 and SiH4. Therefore, Ge and Si are suitable n-type dopants for GaN.

Low-resistivity p-type GaN films, which were obtained by N2-ambient thermal annealing or low-energy electron-beam irradiation (LEEBI) treatment, showed a resistivity as high as 1×106 Ω·cm after NH3-ambient thermal annealing at temperatures above 600°C. In the case of N2-ambient thermal annealing at temperatures between room temperature and 1000°C, the low-resistivity p-type GaN films showed no change in resistivity, which was almost constant between 2 Ω·cm and 8 Ω·cm. These results indicate that atomic hydrogen produced by NH3 dissociation at temperatures above 400°C is related to the hole compensation mechanism. A hydrogenation process whereby acceptor-H neutral complexes are formed in p-type GaN films was proposed. The formation of acceptor-H neutral complexes causes hole compensation, and deep-level and weak blue emissions in photoluminescence.

Low-resistivity p-type GaN films were obtained by N2-ambient thermal annealing at temperatures above 700°C for the first time. Before thermal annealing, the resistivity of Mg-doped GaN films was approximately 1×106 Ω·cm. After thermal annealing at temperatures above 700°C, the resistivity, hole carrier concentration and hole mobility became 2 Ω·cm, 3×1017/cm3 and 10 cm2/V·s, respectively. In photoluminescence measurements, the intensity of 750-nm deep-level emissions (DL emissions) sharply decreased upon thermal annealing at temperatures above 700°C, as did the change in resistivity, and 450-nm blue emissions showed maximum intensity at approximately 700°C of thermal annealing.

High-power p-n junction blue-light-emitting diodes (LEDs) were fabricated using GaN films grown with GaN buffer layers. The external quantum efficiency was as high as 0.18%. Output power was almost 10 times higher than that of conventional 8-mcd SiC blue LEDs. The forward voltage was as low as 4 V at a forward current of 20 mA. This forward voltage is the lowest ever reported for GaN LEDs. The peak wavelength and the full width at half-maximum (FWHM) of GaN LEDs were 430 nm and 55 nm, respectively.

Mg-doped GaN films were grown with GaN buffer layers on a sapphire substrate. Hall-effect measurement of as-grown GaN films showed that the hole concentration was 2×1015/cm3, the hole mobility was 9 cm2/V·s and the resistivity was 320 Ω·cm at room temperature. After the low-energy electron-beam irradiation (LEEBI) treatment, each value became 3×1018/cm3, 9 cm2/V·s and 0.2 Ω·cm at room temperature, respectively. This value of the hole concentration is the highest ever reported for the p-type GaN films and that of the resistivity is the lowest.