AlN GaN Research Articles

Al 预沉积层对金属有机物化学气相沉积方法在 Si 衬底上生长 AlN 缓冲层和 GaN 外延层的影响

Al 预沉积层对金属有机物化学气相沉积方法在 Si 衬底上生长 AlN 缓冲层和 GaN 外延层的影响

Heteroepitaxial Integration of ZnGeN2 on GaN Buffers Using Molecular Beam Epitaxy

Recently theorized hybrid II-IV-N2/III-N heterostructures, based on current commercialized (In,Ga)N devices, are predicted to significantly advance the design space of highly efficient optoelectronics in the visible spectrum, yet there are few epitaxial studies of II-IV-N2 materials. In this work, we present heteroepitaxial ZnGeN2 grown on GaN buffers and AlN templates. We demonstrate that a GaN nucleating surface is crucial for increasing the ZnGeN2 crystallization rate to combat Zn desorption, extending the stoichiometric growth window from 215 °C on AlN to 500 °C on GaN buffers. Structural characterization reveals well-crystallized films with threading dislocations extending from the GaN buffer. These films have a critical thickness for relaxation of 20–25 nm as determined by reflection high energy electron diffraction (RHEED) and cross-sectional scanning electron microscopy (SEM). The films exhibit a cation-disordered wurtzite structure, with lattice constants a = 3.216 ± 0.004 Å and c = 5.215 ± 0.005 Å determined by RHEED and X-ray diffraction (XRD). This work demonstrates a significant step toward the development of hybrid ZnGeN2-GaN integrated devices.

Displacement Talbot lithography for nano-engineering of III-nitride materials

Nano-engineering III-nitride semiconductors offers a route to further control the optoelectronic properties, enabling novel functionalities and applications. Although a variety of lithography techniques are currently employed to nano-engineer these materials, the scalability and cost of the fabrication process can be an obstacle for large-scale manufacturing. In this paper, we report on the use of a fast, robust and flexible emerging patterning technique called Displacement Talbot lithography (DTL), to successfully nano-engineer III-nitride materials. DTL, along with its novel and unique combination with a lateral planar displacement (D2TL), allow the fabrication of a variety of periodic nanopatterns with a broad range of filling factors such as nanoholes, nanodots, nanorings and nanolines; all these features being achievable from one single mask. To illustrate the enormous possibilities opened by DTL/D2TL, dielectric and metal masks with a number of nanopatterns have been generated, allowing for the selective area growth of InGaN/GaN core-shell nanorods, the top-down plasma etching of III-nitride nanostructures, the top-down sublimation of GaN nanostructures, the hybrid top-down/bottom-up growth of AlN nanorods and GaN nanotubes, and the fabrication of nanopatterned sapphire substrates for AlN growth. Compared with their planar counterparts, these 3D nanostructures enable the reduction or filtering of structural defects and/or the enhancement of the light extraction, therefore improving the efficiency of the final device. These results, achieved on a wafer scale via DTL and upscalable to larger surfaces, have the potential to unlock the manufacturing of nano-engineered III-nitride materials.

Strongly Confined Excitons in GaN/AlN Nanostructures with Atomically Thin GaN Layers for Efficient Light Emission in Deep-Ultraviolet.

Fascinating optical properties governed by extremely confined excitons have been so far observed in 2D crystals like monolayers of transition metal dichalcogenides. These materials, however, are limited for production by epitaxial methods. Besides, they are not suitable for the development of optoelectronics for the challenging deep-ultraviolet spectral range. Here, we present a single monolayer of GaN in AlN as a heterostructure fabricated by molecular beam epitaxy, which provides extreme 2D confinement of excitons, being ideally suited for light generation in the deep-ultraviolet. Optical studies in the samples, supplemented by a group-theory analysis and first-principle calculations, make evident a giant enhancement of the splitting between the dark and bright excitons due to short-range electron-hole exchange interaction that is a fingerprint of the strongly confined excitons. The practical significance of our results is in the observation of the internal quantum yield of the room-temperature excitonic emission as high as ∼75% at 235 nm.

(Invited) Advances in Ion Implantation of GaN and AlN

Ion implantation is one of the basic tools for semiconductor device fabrication and as such any maturing semiconductor system should be capable of being processed in this form. Currently, III-nitrides dot not possess a robust ion implantation toolbox that allows for reliable implantation control and activation, thus precluding the possibility of pursuing advanced device architectures comparable to those in SiC. This is obvious when trying to advance the capabilities of the III-nitrides for power applications, where the need for proper field managing schemes require spatially distributed doping distributions that can be achieved by ion implantation. Recent advances in ion implantation for the realization n-type AlN and p-type GaN will be discussed. AlN is considered for deep-UV optoelectronics and next generation high power devices due to its ultra wide bandgap. So far, n-type AlN has been achieved by doping with silicon during epitaxial growth. However, achieving high conductivity in n-type AlN is still a major challenge due to self-compensation via DX and vacancy complex formation at equilibrium. This has made it necessary to consider other non-equilibrium based doping methods, such as ion implantation. In this work, doping AlN by Si implantation is considered. Si implantation was realized into AlN homoepitaxial films grown on bulk AlN substrates via metal organic chemical vapor deposition (MOCVD). Samples were implanted with doses ranging between 5x1013and 1x1015cm-2at 100 keV at RT. Although high-temperature annealing is necessary for damage removal, it enables compensating defect formation by vacancy-silicon complex formation favorable at equilibrium as observed in MOCVD grown AlN. Hence point defect control is necessary during annealing. We further demonstrate defect quasi Fermi level (dQFL) control based compensating point defect reduction in Si implanted AlN during damage recovery. Thus, the highest reported n-type conductivity in AlN was achieved. These results show a possible pathway for the realization of n-type AlN for future optoelectronic and power electronic devices. GaN-based high power switches are a promising avenue towards realizing advances in power management. Controlling the selective area doping of both n- and p-type regions is necessary to realize these device structures. Although high n-type carrier concentrations and conductivities in GaN have been reproducibly demonstrated, achieving high p-type conductivity after ion implantation remains a challenge. To prevent the surface decomposition during annealing at these elevated temperatures required for post-implantation anneals, previous efforts have focused on the use of capping layers (e.g. AlN) and/or complicated annealing procedures. In this work we demonstrate the ability to successfully achieve p-type conductivity in GaN films via room temperature Mg implantation and a post-implantation annealing procedure at high pressure (1 GPa). The highest recorded p-type conductivity (~0.1 Ω-1·cm-1) was measured on the Mg implanted GaN film grown on a sapphire substrate and annealed at 1300 °C and 1 GPa. The implantation and annealing conditions that resulted in the highest p-type conductivity were selected to fabricate p-i-njunction diodes by Mg implantation in n-type GaN grown homoepitaxially on Ammono wafers. All these results support the possibility of realizing successful ion implantation in III-nitrides adding to the growing toolbox of capabilities for this technology.

Effect of high‐temperature AlN buffer on anisotropy of semi‐polar (11‐22) GaN with two pressure growth stages

The low-temperature GaN (LT-GaN) and high-temperature AlN (HT-AlN) buffer layers were grown on m -plane sapphire by metal–organic chemical vapour deposition. The following semi-polar (11-22) GaN thin films were deposited under high- and low-pressure growth stages. Anisotropy of (11-22) GaN grown on HT-AlN buffer along two in-planar directions ([11-2-3] and [-1100]) were clearly suppressed, the maximum variation of the X-ray rocking curve full width at half maximum of (11-22) GaN on LT-GaN buffer was 0.2498°, that of (11-22) GaN on HT-AlN buffer was 0.0488°. The X-ray diffraction results of on-axis and off-axis both indicated that the crystal quality of the epitaxial GaN layer with HT-AlN buffer was obviously improved, and surface morphology was much smoother.

Effect of magnetic field and impurities in InAs/GaAs and GaN/AlN self-assembled quantum dots

A theoeritical study on the effect of a magnetic field or impurities on the carries states of self-assembled quantum dots is presented. The magnetic field is applied along the growth direction of the dots, and for comparison two systems are considered, InAs embeded in GaAs, and GaN in AlN. The electronic states and energy are calculated in the framework of the k.p theory in 8 bands including the strain and piezoelectric effects. Zeeman splitting and anticrossings are observed in InAs/GaAs, while the field introduces small changes in the nitrides. It is also included a study about hidrogen-like impurities, which may be negative or positive. It is noted that depending on the type of impurity, the confinement energy of carriers is changed, and the distribution of the probability density of the carriers is affected too.

AlN encapulsated GaN nanowires

GaN/AlN core-shell nanowires (NWs) were synthesized by a Chemical Vapor Deposition (CVD) through two steps method. GaN core nanowire and AlN shell of each core-shell nanowire are uniform and wurtzite hexagonal single crystal structure. The AlN shell epitaxial grow on GaN core nanowire based on gas-solid (VS) mechanism, and they all grow in [001] direction. The PL property of the GaN/AlN core-shell nanowires shows promising application in ultraviolet photoelectric devices.

AlN/GaN Digital Alloy for Mid- and Deep-Ultraviolet Optoelectronics

The AlN/GaN digital alloy (DA) is a superlattice-like nanostructure formed by stacking ultra-thin ( ≤ 4 monolayers) AlN barriers and GaN wells periodically. Here we performed a comprehensive study on the electronics and optoelectronics properties of the AlN/GaN DA for mid- and deep-ultraviolet (UV) applications. Our numerical analysis indicates significant miniband engineering in the AlN/GaN DA by tuning the thicknesses of AlN barriers and GaN wells, so that the effective energy gap can be engineered from ~3.97 eV to ~5.24 eV. The band structure calculation also shows that the valence subbands of the AlN/GaN DA is properly rearranged leading to the heavy-hole (HH) miniband being the top valence subband, which results in the desired transverse-electric polarized emission. Furthermore, our study reveals that the electron-hole wavefunction overlaps in the AlN/GaN DA structure can be remarkably enhanced up to 97% showing the great potential of improving the internal quantum efficiency for mid- and deep-UV device application. In addition, the optical absorption properties of the AlN/GaN DA are analyzed with wide spectral coverage and spectral tunability in mid- and deep-UV regime. Our findings suggest the potential of implementing the AlN/GaN DA as a promising active region design for high efficiency mid- and deep-UV device applications.

Piezoelectric coefficients of bulk 3R transition metal dichalcogenides

The piezoelectric properties of bulk transition metal dichalcogenides (TMDCs) with a 3R structure were investigated using first-principles calculations based on density functional theory combined with the Berry phase treatment. Values for the elastic constant Cijkl, the piezoelectric coefficient eijk, and the piezoelectric coefficient dijk are given for bulk 3R-TMDCs (MoS2, MoSe2, WS2, and WSe2). The piezoelectric coefficients of bulk 3R-TMDCs are shown to be sufficiently large or comparable to those of conventional bulk piezoelectric materials such as α-quartz, wurtzite GaN, and wurtzite AlN.

Effect of Surface Passivation and Substrate on Proton Irradiated AlGaN/GaN HEMT Transport Properties

In this work, we fabricate Van der Pauw structures on AlGaN/GaN high electron mobility transistors (HEMTs) with both SiN and AlN passivation layers and both SiC and GaN substrates to study temperature dependent electron transport properties of 2 dimensional electron gases (2DEG) in as-fabricated and proton irradiated devices. We confirm that using a GaN substrate or AlN passivation layer enhances the mobility particularly at low temperatures, though this enhancement is greatly reduced upon irradiating the samples with high proton fluences. Our results suggest that the sheet density may be affected by Al diffusion in the sample creating electron donating impurities, which freeze out around 200 K and are more prominent in AlN passivated samples and minimized by using a GaN over a SiC substrate. Additionally, we show that a large dose of radiation forms traps in the AlGaN layer, which drop the sheet density at high proton fluences.

Stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy

The stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy (PA-MBE) has been studied. AlN nucleation layer and GaN layer were grown as a function of III/V ratio. GaN/AlN structure is found to form buried cracks when AlN is grown in the intermediate growth regime(III/V∼1)and GaN is grown under N-rich growth regime (III/V<1). The III/V ratio determines the growth mode of the layers that influences the lattice mismatch at the GaN/AlN interface. The lattice mismatch induced interfacial stress at the GaN/AlN interface relaxes by the formation of buried cracks in the structure. Additionally, the stress also relaxes by misorienting the AlN resulting in two misorientations with different tilts. Crack-free layers were obtained when AlN and GaN were grown in the N-rich growth regime (III/V<1) and metal rich growth regime (III/V≥1), respectively. AlGaN/GaN high electron mobility transistor (HEMT) heterostructure was demonstrated on 2-inch SiC that showed good two dimensional electron gas (2DEG) properties with a sheet resistance of 480 Ω/sq, mobility of 1280 cm2/V.s and sheet carrier density of 1×1013 cm−2.

Mechanism of stress control for GaN growth on Si using AlN interlayers

For the purpose of controlling the wafer bow of GaN-on-Si structure, in situ curvature transient during the growth of a GaN layer on an AlN interlayer was investigated systematically by estimating the compressive strain applied to the GaN layer with the progress of the layer growth. The compressive strain was dependent on the morphology of the GaN surface prior to the growth of the AlN interlayer. It was found that the transition sequence from GaN growth to AlN growth induces roughening of the GaN surface and both high NH3 partial pressure and the short transition time were effective for reducing the roughness of the GaN surface beneath the AlN interlayer. The improved transition sequence increased the compressive strain in GaN by a factor of 2.5. The AlN grown at the same temperature as that of GaN was beneficial in both better surface morphology and the reduction of the transition time between GaN growth and AlN growth. With this high-temperature AlN interlayer, its thickness is another important factor governing the compressive strain in GaN. To get AlN relaxed for applying the compressive strain to GaN, the AlN layer should be thicker but too thick layer after relaxation results in surface roughening, which in turn introduces defects to the overlying GaN layer and reduces the compressive strain by partial lattice relaxation of GaN.

Effective approach for accurately calculating individual energy of polar heterojunction interfaces

We propose a direct approach for calculating individual energy of polar semiconductor interfaces using density functional theory calculations. This approach is applied to polar interfaces between group-III nitrides (AlN and GaN) and SiC and clarifies the interplay of chemical bonding and charge neutrality at the interface, which is crucial for the stability and polarity of group-III nitrides on SiC substrates. The ideal interface is stabilized among various atomic arrangements over the wide range of the chemical potential on Si-face SiC, whereas those with intermixing are favorable on C-face SiC. The stabilization of the ideal interfaces resulting in Ga-polar GaN and Al-polar AlN films on Si-face SiC is consistent with experiments, suggesting that our approach is versatile to evaluate various polar heterojunction interfaces as well as group-III nitrides on semiconductor substrates.

The hydride vapor phase epitaxy of GaN on silicon covered by nanostructures

GaN several tens of μm thick has been deposited on a silicon substrate using a two-step hydride vapor phase epitaxy (HVPE) process. The substrates were covered by AlN layers and GaN nanostructures grown by plasma-assisted molecular-beam epitaxy. During the first low-temperature (low-T) HVPE step, stacking faults (SF) form, which show distinct luminescence lines and stripe-like features in the cathodoluminescence images of the cross-section of the layers. These cathodoluminescence features provide an insight into the growth process. During a second high-temperature (high-T) step, the SFs disappear, and the luminescence of this part of the GaN layer is dominated by the donor-bound exciton. For templates consisting of both a thin AlN buffer and GaN nanostructures, the incorporation of silicon into the GaN grown by HVPE is not observed. Moreover, the growth mode of the (high-T) HVPE step depends on the specific structure of the AlN/GaN template, where in the first case, epitaxy is dominated by the formation of slowly growing facets, while in the second case, epitaxy proceeds directly along the c-axis. For templates without GaN nanostructures, cathodoluminescence spectra excited close to the Si/GaN interface show a broadening toward higher energies, indicating the incorporation of silicon at a high dopant level.

Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers.

We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting.

Optical Gain Optimization of Al0.8Ga0.2N-Delta-GaN Quantum Well Laser in Ultraviolet Spectra Using Genetic Algorithm

An AlGaN based quantum well laser with GaN delta layer and AlN barrier layers has been designed and characterized for obtaining electronic and optical characteristics. The band structure was calculated with self-consistent 6-band k.p formalism including valence-band mixing effect, strain and polarization effect. A Genetic Algorithm based optimization has been performed to optimize the optical gain taking well width, delta width and barrier width into consideration. The Optimization of both TE and TM polarized optical gain exhibits good improvement than previously published work. The peak optical gain as obtained in analysis is 3589.5 cm−1 while the peak spontaneous emission rate is 12.94×1028 s-1cm-3eV-1 at 246.89nm for 5×1019cm-3 carrier density. The optimum TE optical gain is found to be 6479.1 cm-1 for 11Å QW with 7Å delta layer at 279nm wavelength and optimum TM gain is found to be 116.95 cm-1 for 20Å QW with 3Å delta layer at 289.8nm wavelength.

(Invited) Reliability and Pulsed I-V Analysis of Vertically-Scaled GaN MIS-Hemts

GaN solid-state power amplifiers are becoming more frequently utilized in RF applications due to their significant power density advantages over conventional III-V semiconductor materials. Development of the core transistor technology, GaN high-electron-mobility transistors (HEMTs), has been the research focus of numerous groups around the globe. One of the most recent thrusts in the community has been to extend the frequency performance of GaN HEMTs to the millimeter wavelength (MMW) range of 30 – 300 GHz. To obtain power gain at these frequencies, device and heterostructure dimensions must be scaled down to minimize electron transit delay. However, this scaling raises the peak electric fields in the device to extremely high levels and often limits the operational voltage range due to excessive leakage current related breakdown. Historical solutions for managing peak electric fields, such as the use of source-connected field plates in microwave HEMTs, are generally avoided due to the excessive parasitic capacitance introduced. Without field-plate management of peak fields, a critical question that remains to be answered is how to achieve reliable high power operation in a MMW GaN device. In our laboratory we have been exploring methods to simultaneously achieve high power gain at MMW frequencies along with high breakdown voltage [1, 2]. This talk will discuss an initial study that has investigated the effect of SiN gate insulator thickness on MMW GaN HEMT reliability. As illustrated in Fig. 1, the heterostructure used in this work consists of an ultra-thin 2.3 nm In0.17Al0.83N / 1 nm AlN barrier, GaN channel and buffer layers grown on SiC by metalorganic chemical vapor deposition. After heterostructure growth, molecular beam epitaxy was used to deposit 1, 3, 5, or 6 nm of SiN gate insulator at 575 °C. Metal-insulator-semiconductor (MIS) HEMTs with 120 nm gate length were then fabricated using standard processing procedures described previously [2]. For the 5 nm SiN sample, an SF6 plasma recess etch was performed prior to gate metallization, creating a Schottky gate variant as a reference device. After initial dc, pulsed, and RF electrical testing, devices from each sample were biased in class AB at VDS = 20 V on a Maury on-wafer load-pull system that had been tuned to achieve maximum output power. To perform RF operation life testing (RFOL), large signal input power at 40 GHz was set to achieve peak power-added-efficiency while output power (Pout) and drain current were monitored as a function of time. Fig. 2 shows the change in Pout over time for pairs of samples with different gate insulator thickness. Interestingly, samples with thicker SiN showed less degradation in Pout relative to initial values. The dc characteristics of the 6 nm SiN sample before and after stress are shown in Fig. 3. This talk will discuss the measured results and implications for future MMW GaN HEMT design. Acknowledgements: The authors thank N. Green for his assistance with device fabrication. This work was supported by the Office of Naval Research (P. Maki).

A Novel Approach to Improve Heat Dissipation of AlGaN/GaN High Electron Mobility Transistors with a Backside Cu Via

AlGaN/GaN HEMTs have gained more attention recently because of the superior mobility (~1400 cm2/V-s) and high breakdown voltage. However, there still are issues such as self- heating effect, current collapse. HEMTs are grown on sapphire, SiC or Si substrate. Of all the substrates, sapphire is the most common one. However, it is not compatible with the current Si technology. To grow HEMTs on Si, transition layer, grading AlGaN layer, was necessary to overcome the lattice mismatch between Si and GaN. This grading layer provided an additional resistive layer to HEMTs, making the self-heating effect more severe. Several studies have been done to understand the thermal behavior of HEMTs. However, none of them provide a method to increase the thermal dissipation. In this study, we propose a new structure by adding a backside Cu via under active area and demonstrate the thermal dissipation capability by simulation. The structure used in the model consisted of a 25 nm AlGaN barrier layer, a 0.8 µm GaN buffer layer, a 1.4 µm AlGaN transition layer and a 28 nm AlN nucleation layer on 100 µm Si substrate. The LDS was 4 µm. The LG and WG were 0.45 and 100 µm, respectively. For reference, a square through wafer via of 50 µm ×50 µm was placed under the source pad. For our new approach, another rectangular through Si via of 6 µm× 110 µm was opened beneath the active area. Both via holes were filled with copper. Figure 1 showed the temperature distribution along the source and drain direction. For the reference, the maximum junction temperature (Tmax) was 146oC, while 120oC for the new structure. The reduction of Tmax was attributed by the reduction of the thermal resistance, which is a combination effect of nucleation layer removal and filled Cu via. Figure 2 showed vertical temperature distributions in the region directly under the gate for the reference and the new structure. In this figure one can find the temperature drop in each layer. The dimensions of the top AlGaN layer and 2DEG are too thin and the temperature changes across these regions are too small to be observed. For the reference, the temperature drops across the GaN layer, AlGaN layer and AlN layer were 9, 64 and 6°C, respectively. Although the defective AlN layer was only 28 nm, there is an obvious 6°C drop due to its high thermal resistivity. In the case where the defective AlN layer under the active layer was removed and the via was filled up with copper, not only was the Tmax much lower than the reference, but also the temperature at the bottom of the transition layer was 10°C lower than the reference. This indicates the effectiveness of heat removal from the copper filled via. Figure 3 showed the relationship between Tmax with power consumption. As shown in Figure 3, Tmax is directly proportional to power consumption. For the reference, the Tmax increased rate was around 27°C/W while 22°C/W for the new structure. The effect of the copper thickness inside the via on the Tmax was also investigated. From Figure 3, the temperature increase rate was 24°C/W and 23 °C/W of 2 and 1 µm filled Cu via device respectively. The effect of the dimensions of the via on the Tmax were also studied. The results so far were based on the via covering the regions of 4 µm between source and drain contacts as well as 1 µm of the transfer length on each side of the Ohmic metal. The majority of the heat generation of the HEMT is in these two regions. Thus the Tmax increased dramatically when the opening of the via is symmetrically decreased around the gate, as shown in the region I in Figure 4. Region II showed the impact of expanding the width of the via under the source Ohmic metal contact on the Tmax. The Tmax continuously decreased as the width of the via increases due to larger areas of thermal resistive layer being removed and replaced with a less resistive copper layer. The Tmax can be further reduced by extending the via to the drain contact, as shown in region III. In summary, a new approach of implementing a via under the active area of HEMT is proposed to reduce the maximal junction temperature. The via provided a way to remove the highly defective layer and replace it with metal. Because of the reduced thermal resistance, the maximum junction temperature can be significantly decreased from 146 ºC to 120ºC. Figure 1

Electronic structure and optical properties of nonpolar Ga0.75Al0.25N surfaces

In order to study the nonpolar Ga0.75Al0.25N surfaces theoretically, models of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are built. Surface morphology, surface energy, work function, band structure, density of state, and optical properties of the two nonpolar surfaces are calculated using first principle based on density function theory (DFT). Results show that the N atoms and Ga(Al) atoms are not in the same height for both Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces. The GaN and AlN bonds rotate with the N atoms outwards, and the length of GaN bond and AlN bond decrease compared with that of bulk. The surface energy values of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are 1.902J/m2 and 2.014J/m2 respectively. The work function values of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are 4.025eV and 4.007eV respectively. The absorption coefficients of nonpolar surfaces are lower than that of bulk Ga0.75Al0.25N. This work provides a theoretical basis for the design and preparation of Ga1−xAlxN photocathodes.