Search

V-defects are morphological defects that typically form on threading dislocations during epitaxial growth of (0001) -oriented GaN layers. A V-defect is a hexagonal pyramid-shaped depression with six { 10 1 ¯ 1 } -oriented sidewalls. These semipolar sidewalls have a lower polarization barrier than the polarization barriers present between the polar c-plane quantum wells and quantum barriers and can laterally inject carriers directly into quantum wells in GaN-based light emitting diodes (LEDs). This is especially important, as the high polarization field in c-plane GaN is a significant factor in the high forward voltage of GaN LEDs. The optimal V-defect density for efficient lateral carrier injection in a GaN LED (∼109 cm−2) is typically an order of magnitude higher than the threading dislocation density of GaN grown on patterned sapphire substrates (∼108 cm−2). Pure-edge dislocation loops have been known to exist in GaN, and their formation into large V-defects via low-temperature growth with high Si-doping has recently been studied. Here, we develop a method for pure-edge threading dislocation half-loop formation and density control via disilane flow, growth temperature, and thickness of the half-loop generation layer. We also develop a method of forming the threading dislocation half-loops into V-defects of comparable size to those originating from substrate threading dislocations. [ABSTRACT FROM AUTHOR]

The large polarization barriers between the quantum wells and quantum barriers in long-wavelength GaN-based light-emitting diodes (LEDs) inhibit their performance by requiring excess driving voltages to reach standard operating current densities. Lateral injection of carriers directly into quantum wells is required to circumvent this issue. V-defects are naturally occurring inverted hexagonal defects with semipolar 10 1 ¯ 1 -plane sidewalls generated on surface depressions from threading dislocations. LEDs engineered to intentionally generate V-defects below the active region of the LED can achieve lateral carrier injection through the V-defect sidewalls and have already been able to demonstrate world record wall-plug efficiencies for LEDs in the green-red wavelengths. V-defects can be enlarged during kinetically limited growth where the growth rate of the c-plane GaN is faster than that of their sidewalls, leaving them unfilled. We report on the metal organic chemical vapor deposition growth conditions required to fill in V-defects with p-GaN during epitaxial growth of the LED post the active region. Circular transmission length measurements of Pd/Au contacts processed on p-GaN surfaces with various amounts of unfilled V-defects showed no significant difference in their sheet resistance and specific contact resistance. J–V measurements of LEDs grown with varying unfilled V-defect densities showed no significant difference in the forward bias regime. However, in the reverse bias regime, catastrophic breakdown occurred at markedly lower voltages for samples with larger unfilled V-defect densities. This suggests that unfilled V-defects may act as hotspots for device failure, and planarizing LED surfaces may help prevent early degradation of LED devices. [ABSTRACT FROM AUTHOR]

We investigate the unexpected high-energy electroluminescence (EL) peaks observed in long-wavelength InGaN light-emitting diodes (LEDs) with ground state emission peaks between ∼495 and 685 nm by studying the EL spectra of LEDs with varying quantum well (QW) thicknesses and indium compositions. In addition to the ground state emission, two high-energy emission peaks were observed in the LEDs with thick QWs and high indium compositions. The less energetic high-energy emission peak (2.4–2.6 eV) is attributed to the optical transitions involving excited states. Factors influencing the excited state transitions, such as the QW thickness and indium compositions, were also examined by simulations to better understand the occurrence of these transitions. The more energetic high-energy emission peak (2.8–3.1 eV) originates from V-defect sidewalls and was verified through micro-photoluminescence measurements. Identification of the high-energy emission peaks is essential as it enables targeted epitaxial or growth optimizations to minimize or eliminate these undesirable emission peaks. This work demonstrates the importance of using thin QWs to suppress the unwanted high-energy emissions due to excited state transitions and V-defect sidewalls for long-wavelength InGaN LEDs. [ABSTRACT FROM AUTHOR]

The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n+ GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n+ GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditions that varied either the UID GaN NH3 flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV-1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ~11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence. [ABSTRACT FROM AUTHOR]

Vertical β-Ga2O3 Schottky diodes from metal-organic chemical vapor deposition (MOCVD)-grown epitaxial films are reported in this paper for high-power application devices. The Schottky diode, fabricated with a field termination structure, showed a low differential specific on-resistance of 0.67 mΩ cm2. Furthermore, the MOCVD-grown β-Ga2O3 vertical Schottky diodes exhibited a punch-through breakdown and a higher Baliga's figure-of-merit compared to those from other epitaxial growth methods of similar drift layer thickness. This suggests that the MOCVD growth, supporting high-quality epitaxy, can be promising for high-performance β-Ga2O3-based high-power devices. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the detailed optimization of metalorganic chemical vapor deposition (MOCVD)-grown tunnel junctions (TJs) utilizing selective area growth (SAG) for regular size (0.1 mm2) and micro-size InGaN light-emitting diodes (LEDs and µLEDs). Finite-difference time-domain simulations show that the SAG apertures result in a more directional light emission of far-field radiation pattern for the SAG TJ LEDs grown on patterned sapphire substrate. Moreover, it is noted that the n-InGaN insertion layer and Si-doped concentration in the n+GaN TJs layer is essential to realize a low forward voltage (Vf) in TJs LEDs. For both 0.1 mm2 LEDs and µLEDs, the Vf is independent on the SAG aperture space varied from 3 to 8 µm when the Si-doping level in the n+GaN layer is as high as 1.7 × 1020 cm−3. The optimized TJ LEDs exhibit a comparable differential resistance of 1.0 × 10−2 Ω cm2 at 100 A cm−2 and a very small voltage penalty of 0.2–0.3 V compared to the conventional indium tin oxide contact LEDs. The low Vf penalty is caused by a higher turn on voltage, which is the smallest one among the MOCVD-grown TJs LEDs and comparable to the best molecular beam epitaxy-grown TJs LEDs. [ABSTRACT FROM AUTHOR]

Semipolar oriented laser diodes (LDs) have fundamental advantages over c-plane oriented LDs, however, the thickness and composition of InGaN waveguiding layers and AlGaN cladding are limited by the onset of stress relaxation via threading dislocation glide on the c-plane slip system. Limited area epitaxy minimizes misfit dislocation (MD) formation by preventing pre-existing TDs from entering a patterned mesa. We examine the effects of mesa height and facet evolution for LAE grown strained layers. Significant MD formation was suppressed by at least a factor of four for Al0.1Ga0.9N/GaN superlattices, enabling AlGaN-clad structures similar to those used in c-plane LDs. We then demonstrate AlGaN-clad blue (456 nm) LDs with threshold current density (Jth) of 4.5 kA/cm2 and GaN-clad true green (523 nm) LDs with Jth of 12 kA/cm2. TEM measurements of the green LD confirm reduction of MD densities with reduction of MD run length. LAE is effective for improving the optical confinement factor of semipolar LDs and offers a glimpse of the design space that may soon be available using low TD density bulk GaN substrates. [ABSTRACT FROM AUTHOR]

Sn doping of (010) β-Ga2O3 grown by conventional plasma-assisted molecular beam epitaxy (PAMBE) and via metal oxide catalyzed epitaxy (MOCATAXY) using a supplied indium flux during molecular beam epitaxy (MBE) growth was investigated. While high Sn concentrations were achievable over a range of growth conditions in conventional PAMBE, Sn doping less than 1019 cm−3 resulted in non-uniform doping profiles for constant Sn cell temperatures, as well as run-to-run variation in doping. Sn doping in MOCATAXY grown β-Ga2O3 allowed for sharp doping profiles and a wide range of donor concentrations from 3.9 × 1016 cm−3 to 2 × 1019 cm−3 and a maximum room temperature Hall mobility of 136 cm2/V s at 3.9 × 1016 cm−3. From temperature-dependent Hall measurements, Sn was found to have a relatively deep donor state at 77 meV below the conduction band edge. The samples showed low electron mobility at cryogenic temperatures, suggesting the existence of high background impurity levels in the MBE grown films and the need for impurity control in the oxide MBE growth environment. [ABSTRACT FROM AUTHOR]

Epitaxial growth of β-Ga2O3 films on (110) substrates has been performed via plasma-assisted molecular beam epitaxy (PAMBE). The atomic force microscopy scan shows a very low root mean square roughness of 0.08 nm for the surface of the as-received (110) substrates. High-resolution x-ray diffraction measurements reveal a 2.5 nm/min growth rate of β-Ga2O3 films on (110) substrates for conventional PAMBE growth conditions (∼700 °C), which is comparable to that on (010) substrates. The surface morphology of β-Ga2O3 epitaxial films is smooth and has a similar dependence on Ga flux to (010) growth. However, the (110) plane does not have a tendency to show a well-defined step–terrace structure in spite of the appearance of (110) facets in the growth of (010) β-Ga2O3. Indium catalyzed growth was also demonstrated to improve the growth rate up to 4.5 nm/min and increase the maximum growth temperature up to 900 °C of (110) β-Ga2O3. [ABSTRACT FROM AUTHOR]

Mid-infrared intersubband transitions are investigated in nonpolar m-plane and a-plane GaN/AlGaN multi-quantum well heterostructures. Nominally identical heterostructures were grown by ammonia molecular-beam epitaxy on free-standing m-plane and a-plane GaN substrates. A total of 12 well- and barrier-doped samples with intersubband transition energies in the range of 220–320 meV (wavelength range 3.8–5.6 μm) were grown. The intersubband absorption lines of the m-plane samples were 10–40% narrower than those of the a-plane samples, and a very narrow intersubband absorption linewidth of 38 meV (full width at half maximum) at a transition energy of approximately 250 meV (5 μm wavelength) was observed in an m-plane sample. Narrower intersubband absorption linewidths of m-plane samples can be explained by more abrupt heterostructure interfaces revealed by structural characterization, which is attributed to a higher stability of the m-plane compared to the a-plane. No significant difference in the intersubband absorption linewidth was observed between the barrier- and well-doped samples. [ABSTRACT FROM AUTHOR]

We describe the development of N-polar GaN-based high electron mobility transistors grown by N2 plasma-assisted molecular beam epitaxy on C-face SiC substrates. High mobility AlGaN/GaN modulation-doped two-dimensional electron gas channels were grown, and transistors with excellent dc and small-signal performance were fabricated on these wafers. Large-signal dispersion was observed, and the trap states responsible for this were identified, and layer designs to remove the dispersive effects of these traps were demonstrated. Finally, an AlGaN-cap layer was used to reduce gate leakage in these devices, and a low-dispersion high breakdown voltage device was achieved. This detailed study of dispersion and leakage in N-polar GaN-based transistors establishes a technological base for further development of field effect devices based on N-polar III-nitrides. [ABSTRACT FROM AUTHOR]

We have investigated the adsorption and subsequent desorption of Ga on (0001) GaN using simultaneous line-of-sight quadrupole mass spectrometry (QMS) and reflection high-energy electron diffraction (RHEED). The in situ QMS and RHEED desorption transient measurements demonstrate the Ga flux dependent accumulation of the theoretically predicted laterally contracted Ga bilayer [J. E. Northrup et al., Phys. Rev. B 61, 9932 (2000)] under conditions similar to those used during GaN growth by rf-plasma molecular beam epitaxy. We correlated bioscillatory RHEED desorption transients [C. Adelmann et al., J. Appl. Phys. 91, 9638 (2002)] to QMS-measured Ga-adsorbate coverage and found both to be consistent with layer-by-layer desorption of the Ga-adsorbate bilayer. The QMS-measured steady-state Ga-adlayer coverage exhibited a continuous increase from 0 to 2.4 ML (monolayer) with respect to impinging Ga flux at substrate temperatures of 640–700 °C. We observed an exponential dependence of the Ga flux corresponding to 1.0 ML Ga-adsorbate coverage on substrate temperature and we measured an apparent activation energy of 2.43±0.11 eV and an attempt prefactor of 6.77×1012 nm/min (4.36×1011 Hz) for this transition. [ABSTRACT FROM AUTHOR]

Transition metals, such as Fe, are commonly used in either layers or substrates to serve as deep intentional acceptors to realize semi-insulating substrates, regrowth interfaces, or buffer layers. The unintentional incorporation of the compensating acceptor in subsequent layers is a major concern in epitaxial growth. In this paper, we report on unintentional Fe incorporation for the homoepitaxial growth of (010) β-Ga2O3 by plasma-assisted molecular beam epitaxy on (010) Fe-doped β-Ga2O3 substrates. Fe was found to incorporate heavily into films grown at 500 °C, while growth temperatures of 650 °C and higher showed a significantly longer tail of Fe in the films. This Fe tail was determined to be a result of surface riding during growth rather than diffusion. The total surface riding concentration of Fe was found to be approximately 3 × 1012 cm−2 from a typical Fe-doped (010) β-Ga2O3 substrate. Surface segregation coefficients of 0.982 and 0.993 were calculated for growth temperatures of 500 °C and 700 °C, respectively. Furthermore, growth temperatures of 500 °C–700 °C demonstrated high crystalline quality and smooth surface morphology. [ABSTRACT FROM AUTHOR]

Group III impurity doped ZnO thin films were deposited on MgAl2O3 substrates using a simple low temperature two-step deposition method involving atomic layer deposition and hydrothermal epitaxy. Films with varying concentrations of either Al, Ga, or In were evaluated for their optoelectronic properties. Inductively coupled plasma atomic emission spectroscopy was used to determine the concentration of dopants within the ZnO films. While Al and Ga-doped films showed linear incorporation rates with the addition of precursors salts in the hydrothermal growth solution, In-doped films were shown to saturate at relatively low concentrations. It was found that Ga-doped films showed the best performance in terms of electrical resistivity and optical absorbance when compared to those doped with In or Al, with a resistivity as low as 1.9 mΩ cm and an optical absorption coefficient of 441 cm−1 at 450 nm. [ABSTRACT FROM AUTHOR]

A PAMBE (plasma-assisted molecular beam epitaxy) growth diagram of InGaN is established for the metal-face (0001) orientation at 575 °C. This growth diagram allows identifying different growth regimes during the epitaxy of InGaN, namely the N-rich, the Ga-rich, the intermediate In-rich, and the In-accumulation regimes. InGaN compositional grades are then grown by ramping the Ga and In fluxes in parallel to remain in either the intermediate In-rich or the N-rich regime. The two samples exhibit distinct structural characteristics, surface morphologies, and optical properties. The growth diagram proves to be a useful tool in controlling the metal fluxes and thereby the stoichiometry conditions on the surface during the growth of compositionally graded layers. [ABSTRACT FROM AUTHOR]

Atom probe tomography was used to characterize AlN interlayers in AlGaN/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy (PAMBE), NH3-based molecular beam epitaxy (NH3-MBE), and metal-organic chemical vapor deposition (MOCVD). The PAMBE-grown AlN interlayer had the highest purity, with nearly 100% of group-III sites occupied by Al. The group-III site concentrations of Al for interlayers grown by NH3-MBE and MOCVD were ∼85% and ∼47%, respectively. Hall measurements were performed to determine the two-dimensional electron gas mobility and sheet concentration. Sheet concentrations were ∼25%-45% higher with molecular beam epitaxy than with MOCVD, and these results matched well with atom probe data. [ABSTRACT FROM AUTHOR]

In this study, a-plane GaN was grown on r-plane sapphire by sidewall lateral epitaxial overgrowth. Prismatic stacking faults (PSFs) in the window region of the GaN layer were identified to have an atomic configuration similar to the model presented by Northrup [Appl. Phys. Lett. 72, 2316 (1998)], which was demonstrated by comparing high-angle annular dark-field scanning transmission electron microscopy images with the atomic configurations of the Drum model, the Amelinckx model, and simplified Northrup model, respectively. The Northrup PSF structure has been further confirmed by the scattering contrast analysis in transmission electron microscopy experiments. [ABSTRACT FROM AUTHOR]

Cathodoluminescence imaging was used to study the onset of plastic relaxation and critical thickness for misfit dislocation (MD) formation by basal plane (BP) or nonbasal plane (NBP) slip in In0.09Ga0.91N/GaN heterostructures grown on nonpolar [formula] and semipolar [formula] substrates. Layers grown on both orientations were shown to stress relax initially via generation of NBP MDs as a result of prismatic slip on inclined m-planes. Analysis of the resolved shear stress on the two slip planes (i.e., basal and an inclined m-plane) reveals a crossover at which the resolved shear stress on the m-planes becomes larger than that on the BP. [ABSTRACT FROM AUTHOR]

The authors demonstrate the heteroepitaxial and homoepitaxial growth of single crystalline β-Ga2O3 by plasma-assisted molecular beam epitaxy. Phase-pure (201) and (100) β-Ga2O3 thin films were grown on c-plane sapphire and (100) β-Ga2O3 substrates, respectively. Based on the homoepitaxial results, detailed information is reported on the dependence between the β-Ga2O3 film quality and various growth parameters. At an optimized growth temperature of 700 °C, a growth relationship between growth rates and increasing gallium fluxes was established at a fixed oxygen pressure. A three-dimensional columnar growth with a relatively high growth rate was measured at a low gallium flux while a terrace surface morphology with a reduced growth rate was observed as the gallium flux increased. The gallium flux played an important role on both surface morphology and growth rate. We associated the decreasing growth rate with increasing gallium flux with the formation of gallium suboxides monitored by quadrupole mass spectrometry. The formation and desorption of volatile gallium suboxides limited the resulting growth rate of β-Ga2O3 growth. [ABSTRACT FROM AUTHOR]

A quantitative mobility spectrum analysis (QMSA) of multiple magnetic field data has been used to determine the transport properties of bulk and surface electron species in InN films, grown by plasma-assisted molecular beam epitaxy (PAMBE) with varying substrate temperatures and In/N flux ratios. While all films have similar bulk electron densities, ~4 x 1017 cm-3, the highest mobility was obtained in the highest growth temperature film (3100 cm²/V s at 150 K), while In-rich growth also gave good mobility values even at a much lower growth temperature. The surface sheet electron concentration increased with surface roughness, which increased with N-flux during growth. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) was used to study the onset of mechanical stress relaxation in low indium composition semipolar [formula] InxGa1-xN lattice-mismatched layers grown on bulk GaN substrates. Monochromatic CL of short interfacial misfit dislocation (MD) segments showed a single threading dislocation (TD) associated with each MD segment-demonstrating that the initial stage of MD formation in semipolar III-nitride heterostructures proceeded by the bending and glide of pre-existing TDs on the (0001) slip plane. The state of coherency as determined by panchromatic CL is also compared to that determined by x-ray diffraction analysis based on crystallographic epilayer tilt and Matthew-Blakeslee's critical thickness calculations. [ABSTRACT FROM AUTHOR]

Coalesced, crack-free (0001) AlN films were grown on stripe patterned sapphire substrates without AlN seed layers using hydride vapor phase epitaxy. Using templates with stripes oriented in the [formula] direction, lateral epitaxial overgrowth AlN films were coalesced over trench regions as wide as 10 μm despite parasitic sidewall and trench growth. Using transmission electron microscopy, a reduction in the dislocation density from 1.6×109 cm-2 in the seed region to less than 1.0×108 cm-2 in the wing region was demonstrated. Atomic force microscopy and cathodoluminescence measurements were also performed to assess the material quality. [ABSTRACT FROM AUTHOR]

Sidewall lateral epitaxial overgrowth (SLEO) is demonstrated by metal organic chemical vapor deposition for nonpolar [formula] m-plane GaN films. m-plane GaN films were grown by metal organic chemical vapor deposition on m-plane 6H SiC substrates with an AlN initiation layer. Subsequently, an SiO2 stripe dielectric pattern was formed with 2 μm window openings parallel to the [1120] a-direction and an 8 μm mask and then the m-plane GaN was etched through the window openings to reveal Ga-face (0001) and N-face (0001) sidewalls. The SLEO growth was achieved in two growth steps—lateral growth from the sidewalls and subsequent growth through and then over the dielectric mask openings. In comparison to planar m-plane GaN films grown on 6H SiC, the threading dislocation density was reduced from low 1010 to 3×108 cm-2 and the stacking fault density was reduced by one order of magnitude. [ABSTRACT FROM AUTHOR]

This letter reports on the reduction of threading dislocation densities in AlN films via lateral epitaxial overgrowth by hydride vapor phase epitaxy. A variety of different stripe patterns were used to produce fully coalesced AlN films. Transmission electron microscopy (TEM) was used to assess the structural quality of these films. TEM determined that the dislocation density in the laterally grown wing regions was less than 8.3×106 cm-2 as compared to 1.8×109 cm-2 in the seed regions. Atomic force microscopy revealed that the films have a smooth surface morphology with a rms roughness of 0.71 nm over 10×10 μm2 sampling areas. [ABSTRACT FROM AUTHOR]

We demonstrate a technique to reduce the extended defect densities in a-plane GaN deposited on r-plane sapphire. The SiO2 lateral epitaxial overgrowth mask consisted of ⟨1100㟩GaN stripes. Both the mask and GaN were etched through the mask openings and the lateral growth was initiated from the etched c-plane GaN sidewalls, and the material was grown over the mask regions until a smooth coalesced film was achieved. Threading dislocation densities in the range of 106–107 cm-2 were realized throughout the film surface. The on-axis and off-axis full width at half maximum value and surface roughness were 0.082°, 0.114°, and 0.622 nm, respectively. [ABSTRACT FROM AUTHOR]

We studied the effect of extended defects on electrical characteristics of Si doped n-type nonpolar a-plane GaN films. The n-type GaN layers were grown on co-loaded reduced defect density sidewall lateral epitaxial overgrowth (SLEO) a-plane GaN templates and high defect density planar a-plane GaN templates by metalorganic chemical vapor deposition (MOCVD). The highest conductivity value was observed at the carrier concentration of 1.05 x 1019 cm-3 as 261.12 cm2/Vs for SLEO a-GaN and 106.77 cm2/Vs for the planar a-plane GaN samples. At the same doping level, the carrier compensation for SLEO samples was ~12% less than planar samples. [ABSTRACT FROM AUTHOR]

We demonstrate the growth of epitaxial (100)-oriented, rutile Sb-doped SnO 2 (ATO) and (111)-oriented, cubic Sn-doped In 2 O 3 (ITO) transparent conducting oxide (TCO) contacts on top of an InGaN/GaN(0001) light emitting diode (LED) by plasma-assisted molecular beam epitaxy (PAMBE). Both oxides form rotational domains. The in-plane epitaxial alignment of the two ITO(111) rotational domains to the GaN(0001) was: GaN [21-10]|| ITO Domain1 [‐ 211]|| ITO Domain2 [‐ 1‐12]. A growth temperature as low as 600 °C was necessary to realize a low contact resistance between ATO and the top p-GaN layer of the LED but resulted in non-optimal resistivity (3.4 × 10 − 3 Ω cm) of the ATO. The current–voltage characteristics of a processed LED, however, were comparable to that of a reference LED with a standard electron-beam evaporated ITO top contact. At short wavelengths, the optical absorption of ATO was lower than that of ITO, which is beneficial even for blue LEDs. Higher PAMBE growth temperatures resulted in lower resistive ATO but higher contact resistance to the GaN, likely by the formation of an insulating Ga 2 O 3 interface layer. The ITO contact grown by PAMBE at 600 °C showed extremely low resistivity (10 − 4 Ω cm) and high crystalline and morphological quality. These proof-of-principle results may lead to the development of epitaxial TCO contacts with low resistivity, well-defined interfaces to the p-GaN to help minimize contact losses, and enable further epitaxy on top of the TCO. [ABSTRACT FROM AUTHOR]

Abstract: This paper demonstrates the use of Sidewall Lateral Epitaxial Overgrowth (S-LEO) on a-plane GaN thick films on r-plane sapphire by hydride vapor phase epitaxy (HVPE). Comprehensive study of the extended defect microstructure of the a-plane GaN films was carried out using cross-sectional and plan-view transmission electron microscopy (TEM). A very low density of primary threading dislocations and a heterogeneous microstructure can be found in the GaN films. In the window region and N-face wing region, the extended defects included type I1 and type I2 basal stacking faults (BSFs), as well as prismatic stacking faults (PSFs) on a-planes. The density of type I1 BSFs was in the order of ∼2×105 cm−1, type I2 BSFs in the order of ∼104 cm−1, and corresponding localized partial dislocation density less than 1.5×109 cm−2. PSFs on a-planes were connected to two neighboring type I1 BSFs with an estimated density of 3×102 cm−1 in the plan-view images. In the Ga-face overgrowth regions, the density of BSFs was lower than 104 cm−1. However, inversion domains bounded by (11̄02), (11̄02̄), and (11̄00) planes were found in the Ga-face wing regions. The nature of inversion domain boundaries (IDB) on m-planes can be explained by the Auserman-Gehamn model using high-angle annular dark-field TEM images. [Copyright &y& Elsevier]