Nonpolar Orientations Research Articles

Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN

Indium incorporation and the optical properties of InxAl1−xN layers (0 ≤ x ≤ 0.45) grown by metal-organic vapour phase epitaxy have been investigated simultaneously on polar (0001), untwinned semipolar (101̅3) and nonpolar (101̅0) AlN templates, which were prepared on planar sapphire substrates. The InN mole fraction () of the layers was tuned by changing growth temperature from 660°C to 860°C. determined by x-ray diffraction was found to be comparable for the polar, semipolar and nonpolar surface orientations. This is consistent with comparable effective bandgap energy of the layers obtained from optical transmission measurements at room temperature. The bandgap bowing parameter was found to be strongly composition-dependent. Room-temperature photoluminescence measurements showed impurity transitions for the layers with ≤ 0.2, while InAlN near-band-edge luminescence was observed for the layers with higher .

Noise characteristics of Ni/GaN Schottky barrier IMPATT diode based on polar- and nonpolar-oriented wurtzite GaN for terahertz application

Abstract This paper reports a study investigating the noise performance of Ni/GaN Schottky barrier impact-ionization-avalanche-transit-time (IMPATT) diodes based on the polar- and nonpolar-oriented wurtzite GaN by a numerical simulation. Results show that the nonpolar IMPATT diode exhibits a significant wider and higher frequency-band corresponding to the low noise measure (NM). The upper limit of the low-noise frequency-band of the IMPATT diode shifts from 159.2 GHz to 184.3 GHz, from 183.4 GHz to 245.7 GHz and from 212.2 GHz to 285.6 GHz when J0 = 1 kA/cm2, 10 kA/cm2 and 100 kA/cm2, respectively, comparing the polar with the nonpolar IMPATT diodes. Our analysis proves that the mechanism comes from excellent properties of the Negative Differential Mobility (NDM) characteristic in the nonpolar orientation wurtzite GaN. In particular, the nonpolar diode still demonstrates better unity between the noise and RF power performances and can significantly improve the stability of IMPATT diodes at terahertz frequency.

Effects of substrate self-bias and nitrogen flow rate on non-polar AlN film growth by reactive sputtering

The effects of the N2 gas flow ratio and the substrate self-bias of reactive sputtering on the polarity of AlN film on various planar sapphire substrates were investigated to obtain a non-polar oriented AlN film. On a c-plane sapphire substrate, substrate self-bias enhanced c-plane AlN growth and Al termination at the surface, as confirmed by X-ray diffraction (XRD) and time-of-flight low-energy atom scattering spectroscopy. In addition, the AlN film deposited at an N2 gas:Ar sputtering gas ratio of 14% with substrate self-bias had high crystallinity with an XRD ω-rocking curve of 17 arcsec for the 0002 diffraction. In contrast, the AlN films on a- and r-plane sapphire substrates had semi-polar and non-polar plane orientations, respectively. However, on the a-plane sapphire substrate, the c-plane-orientated AlN phase was also observed, which was increased under substrate self-bias condition and an N2 flow rate below 30%. Preferable conditions for non-polar AlN growth by reactive sputtering were non-substrate self-bias and a high N2 flow rate of 30% or more.

A facile and reproducible synthesis of non-polar ZnO homojunction with enlarged rectification rate and colorful light emission

A novel fabrication of non-polar Sb-doped ZnO homojunction was realized via a facile and reproducible low-temperature aqueous solution deposition in the presence of Sb dopant dissolved in ethylene glycol (EG). The undoped non-polar ZnO films were introduced as the non-polar substrates for the non-polar growth of Sb-doped ZnO film as well as the SZO/ZnO homojunction. The parameters including the reaction time and dopant concentration for the synthesis of non-polar SZO/ZnO homojunction were identified. The existence and distribution of Sb dopant in SZO layer were confirmed by X-ray photoelectron spectroscopy (XPS) and elemental mapping analysis. The I–V measurement result indicated the p-type conduction of SZO layer and the synthesized p-SZO/n-ZnO homojunction with non-polar preferred orientations possessed both ultra-low turn-on voltage (1.5 V) and large rectification rate (>105). The excitation of orange-red light emissions from deep-level energy band gap demonstrated the (SbZn-xVZn) complex defect pattern. This novel non-polar SZO/ZnO homojunction could be an excellent candidate for the applications of one-dimensional ZnO nanomaterials in the electronic/photoelectronic field.

Post-annealing induced oxygen vacancy mediated non-polar ZnO films with excellent opto-electronic performance

The considerably enhanced opto-electronic properties of ZnO films with non-polar orientations have been realized by introducing oxygen vacancies. Excitation of oxygen vacancies has been achieved by oxygen-deficient post-annealing treatment. The existence of oxygen vacancies is directly confirmed by cross-sectional XPS and positron annihilation Doppler broadening measurements. An enhanced UV-emission, more simplex green-light emission and sharply decreased electrical resistivity of post-annealed non-polar oriented ZnO films have been acquired in oxygen-deficient atmosphere. I-V measurement indicates that non-polar oriented ZnO/p-Si heterojunction with optimized post-annealing treatment owns an excellent forward electrical transportation and extremely low threshold voltage, have great competitiveness for the commonly used one-dimensional ZnO nanomaterials in photo-electronic field.

Hybrid polar state in epitaxial (111) PbSc0.5Nb0.5O3 relaxor ferroelectric films

In relaxor ferroelectrics, the interplay between the short-range-order dipolar state and long-range-order ferroelectric state leads to outstanding response functions, which enable valuable capacitor, electromechanical, pyroelectric, and electrocaloric applications. Advanced applications are envisaged with epitaxial relaxor ferroelectric films, whose fundamentals are still poorly explored. In particular, frustration of ferroelectricity, contrasting the bulk behavior, has been found and ascribed to nonpolar crystal orientation in (001) epitaxial films of archetypical lead-based relaxors. Here, a peculiar hybrid polar state, where coexisting long-range and short-range orders persist to very low temperatures, is demonstrated in epitaxial polar-oriented (111) ${\mathrm{PbSc}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}$ films. The hybrid state is evidenced by relaxorlike frustrations of ferroelectric transition and the Curie-Weiss behavior, validity of the Vogel-Fulcher relationship, a non-Rayleigh dynamic nonlinearity, and a ferroelectriclike low-temperature polarization. Local fluctuations of lattice strain arising from the relaxation of large epitaxial misfit are suggested to be responsible for the hybrid polar state. Introducing strain fluctuations by doping or nanostructuring is anticipated to boost the dynamic dielectric and piezoelectric performance of many perovskite oxide ferroelectrics.

Effects of composition, crystal structure, and surface orientation on band alignment of divalent metal oxides: A first-principles study

Using first-principles calculations, this paper systematically investigates the ionization potentials (IPs) and electron affinities (EAs) of nonpolar surfaces of binary divalent metal oxides with formally closed-shell electronic structures, namely, BeO, MgO, CaO, SrO, BaO, ZnO, HgO, SnO, and PbO in relevant crystal structures. An emphasis is put on the understanding of the effects of chemical composition, crystal structure, and surface orientation on the surface band positions. Slab models for nonpolar surfaces are automatically generated using a proposed algorithm that provides a set of unique nonpolar surface orientations. A non-self-consistent dielectric-dependent hybrid functional approach is employed that is shown to provide a significant improvement in the band-gap, IP, and EA evaluation over standard density functional theory calculations using the generalized gradient approximation. The valence band maximum, O $2s$ band center, and O-site local potential versus the vacuum level are examined for prototypical rocksalt, wurtzite, and zincblende surfaces of selected systems without atomic relaxation. All of these quantities are found to qualitatively follow the tendency in the Madelung potential at the O site, where decreasing interatomic distance results in deeper energy levels. The valence band maxima versus the vacuum level or the IPs after atomic relaxation also show a similar trend even when other cation species and crystal structures are included in the discussion, while there is much less correlation for EAs. An overall trend indicates that lattice volume reflecting cation species is a determinant factor to the IPs of the divalent metal oxides investigated in this paper although there are surface-specific dipole contributions that cause the surface orientation dependence of the IPs.

Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial ferroelectric films is demonstrated. Scanning transmission electron microscopy (STEM) indicates that the polarization of a pristine film deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization field with respect to the out-of-plane direction. Applying an electric field aids in ferroelastic domain switching in YHO-7 films. Such films exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 μC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90° domain switching as the odd number reflection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a significant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.

Well-ordered ZnO nanowires with controllable inclination on semipolar ZnO surfaces by chemical bath deposition

Controlling the formation of ZnO nanowire (NW) arrays on a wide variety of substrates is crucial for their efficient integration into nanoscale devices. While their nucleation and growth by chemical bath deposition (CBD) have intensively been investigated on non-polar and polar c-plane ZnO surfaces, their formation on alternatively oriented ZnO surfaces has not been addressed yet. In this work, the standard CBD technique of ZnO is investigated on and semipolar ZnO single crystal surfaces. A uniform nanostructured layer consisting of tilted ZnO NWs is formed on the surface while elongated nanostructures are coalesced into a two-dimensional compact layer on the surface. By further combining the CBD with selective area growth (SAG) using electron beam-assisted lithography, highly tilted well-ordered ZnO NWs with high structural uniformity are grown on the patterned surface. The structural analysis reveals that ZnO NWs are homoepitaxially grown along the polar c-axis. The occurrence of quasi-transverse and -longitudinal optical phonon modes in Raman spectra is detected and their origin and position are explained in the framework of the Loudon’s model. These results highlight the possibility to form ZnO NWs on original semipolar ZnO surfaces. It also opens the way for comprehensively understanding the nucleation and growth of ZnO NW arrays on poorly and highly textured polycrystalline ZnO seed layers composed of nanoparticles with a wide range of non-polar, semipolar, and polar plane orientations. Eventually, the possibility to tune both the inclination and dimensions of well-ordered ZnO NW arrays by using SAG on semipolar surfaces is noteworthy for photonic and optoelectronic nanoscale devices.

Pulsed laser deposition and characteristics of epitaxial non-polar m-plane ZnO1-xSx alloy films

Non-polar m-plane ZnO1-xSx (ZnOS) thin films were grown epitaxially on m-plane sapphire using pulsed laser deposition for the first time. Effects of the growth temperature on the surface morphology, as well as on the structural and optical properties of the films were investigated. The S content in the ZnO1-xSx alloy films was adjusted by controlling the substrate temperature. X-ray diffraction analyses revealed that, the ternary ZnO1-xSx films changed from polycrystalline to monocrystalline-like with increasing growth temperature, and m-plane orientated ZnO1-xSx thin films were achieved at temperatures above 400 °C. The films with S content below 28 at% exhibit a unique non-polar (101¯0) orientation. For the films grown at 300 °C with S content above 34 at%, however, additional diffraction peaks from (0002) and (112¯0) planes are present. The φ-scan patterns suggest the following in-plane epitaxial relationship: ZnOS(0001) || sapphire(12¯10) and ZnOS(12¯10) || sapphire(0001). With the S content increasing from 12 at% to 28 at%, the lattice constant a of m-plane ZnO1-xSx films expands monotonically from 3.299 to 3.698 Å, while their optical bandgaps decrease from 3.05 to 2.95 eV. Differing from the c-plane ZnOS films, the m-plane ZnOS films exhibit anisotropic crystalline quality, extended S solubility, and nearly non-bowing bandgap tunability with the S content. This first-hand information is useful for future rational design of m-ZnOS-based junctions and optoelectronic devices.

Deformation and fracture in (0001) and (10-10) GaN single crystals

ABSTRACTIndentation techniques were utilised to induce deformation on polar (0001) c-plane and non-polar m-plane GaN single crystal. Cracking was more sensitively dependent on the orientation of the indenter tip, compared to hardness. The indentation-induced plastic deformation and fracture sequences were studied by cathodoluminescence imaging and optical microscopy, respectively. Polar GaN was harder than non-polar, while pop-in discontinuities occurred at lower loads in polar than non-polar GaN. Dislocation arrangements were more isotropic at the polar than the non-polar orientation. Polar GaN was more susceptible to cracking compared to non-polar. Indentation at the high load regime fostered radial and lateral crack formation at both indenter orientations in polar GaN. Post-indentation lateral crack propagation was observed in situ in polar GaN.This is part of a thematic issue on Nanoscale Materials Characterisation and Modeling by Advances Microscopy Methods - EUROMAT.

(Invited) High-Speed GaN-Based Micro-Scale Light-Emitting Diodes for Visible-Light Communication

The increasing demand for wireless data communication and popularity of solid-state lighting has prompted research into visible-light communication (VLC) systems using GaN-based light-emitting diodes (LEDs). VLC is a promising candidate for next-generation (5G and beyond) light-fidelity (Li-Fi) network systems. To support multi-Gb/s data rates, VLC systems will require efficient LEDs with large modulation bandwidths. Conventional lighting-class LEDs cannot achieve high-speed operation due to their large chip size, large active region volume, and phosphor-converted output. Conversely, micro-scale LEDs (micro-LEDs) offer a viable path to high-speed operation due to their lower parasitic capacitance and ability for operation at high current densities where the carrier lifetime is significantly reduced. Furthermore, conventional c-plane LEDs suffer from polarization-related electric fields, which reduce the overlap between the electron and hole wave functions and lower the carrier recombination rate. Since modulation bandwidth is proportional to the carrier recombination rate (inversely proportional to the carrier lifetime), the overlap between the wave functions should be maximized for high-speed operation. Nonpolar and semipolar orientations have significantly reduced polarization effects and wave function overlaps approaching unity. These orientations can enable high-efficiency LEDs with simultaneously large modulation bandwidths, especially at relatively low current densities. In this work, we introduce VLC and discuss progress on the growth, fabrication, and characterization of high-speed micro-LEDs. Polar (0001), nonpolar (1010), and semipolar (2021) InGaN/GaN micro-LEDs on free-standing GaN substrates are investigated for their small-signal modulation characteristics as a function of current density, temperature, device area, and active region design. We demonstrate that the modulation bandwidths are well correlated with the wave function overlap in the active region by examining the orientation-dependence of the bandwidth. Record modulation bandwidths for GaN-based LEDs above 1 GHz are achieved for the nonpolar and semipolar orientations. We also show the modulation characteristics of an electrically injected nanowire-based LED, which achieves a modulation bandwidth of 1.2 GHz. Finally, we present a small-signal modeling method for determining the RC characteristics, differential carrier lifetime, carrier escape lifetime, and injection efficiency of the LEDs under electrical injection and discuss the results in the context of efficiency droop. Figure 1: Bandwidth vs. current density for the nonpolar LEDs (open black triangles), semipolar LED (open blue circles), and polar c-plane LED (open green squares) compared to other reported polar c-plane LEDs on sapphire or with a flip-chip design and compared to semipolar (1122) LEDs. The bandwidth characteristics for a nanowire-based LED are also included. Also shown are the crystal orientations used in the orientation-dependent bandwidth study. Figure 1

Performance of resonant tunneling diodes based on the nonpolar-oriented AlGaN/GaN heterostructures

The performance of resonant tunneling diodes (RTDs) based on nonpolar-oriented AlGaN/GaN heterostructures has been theoretically investigated by numerical simulation. Simulation results show that the RTDs grown along the nonpolar orientation can yield the current–voltage (I–V) characteristics with the peak current, the peak-to-valley ratio (PVCR), and the peak voltage of about 3.5 times and 1.5 times higher and 1.1 times lower than those of RTDs grown along the conventional polar orientation, respectively. The results also show excellent symmetry, high reproducibility of I–V characteristics, and high intrinsic response frequency.

Role of defect states on nonlinear properties of 8 MeV electrons irradiated zinc oxide thin films under off-resonant regime

In the present work, ZnO thin films were synthesized by sol-gel with subsequent spin coating on corning glass substrates. To understand the variations in the structural, optical, and nonlinear optical properties of ZnO thin films, 8 MeV electron irradiation with different dose rates (0 kGy, 1 kGy, 5 kGy, and 10 kGy) was performed. The XRD spectra showed transition from polar crystal growth orientation to non-polar crystal growth orientation of the films when the irradiation dose rate was increased from 0 kGy to 10 kGy and this was attributed to the reduced thickness of the irradiated films. The generation of localized surface states below the conduction band upon electron irradiation was confirmed by the quantification of the Urbach energy. A large band gap shrinkage was observed in the irradiated films (3.31–3.10 eV) due to the enhanced surface states. The photoluminescence spectra showed reduction in the NBE emission due to the enhanced surface states in the irradiated films. Open aperture and closed aperture Z-scan measurements were performed to extract the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) values using 532 nm Nd:YAG laser having pulse width of 7 ns. The open aperture Z-scan profiles of the films showed the presence of normalized transmittance valley, which was attributed to the two photon absorption (TPA) behaviour. The reduction in the depth of the normalized transmittance valley in irradiated films was ascribed to the bleaching of carriers in the ground states due to their trapping in the defect states. The closed aperture Z-scan curves showed the presence of normalized pre-focal peak, followed by a valley, which is characteristic of the self-defocusing nonlinear refraction behaviour. The electron irradiation with different dose rates provided an opportunity to understand the variations in the optoelectronic properties of the ZnO thin films considering the various defect states generated upon irradiation.

Impact of crystal orientation on the modulation bandwidth of InGaN/GaN light-emitting diodes

High-speed InGaN/GaN blue light-emitting diodes (LEDs) are needed for future gigabit-per-second visible-light communication systems. Large LED modulation bandwidths are typically achieved at high current densities, with reports close to 1 GHz bandwidth at current densities ranging from 5 to 10 kA/cm2. However, the internal quantum efficiency (IQE) of InGaN/GaN LEDs is quite low at high current densities due to the well-known efficiency droop phenomenon. Here, we show experimentally that nonpolar and semipolar orientations of GaN enable higher modulation bandwidths at low current densities where the IQE is expected to be higher and power dissipation is lower. We experimentally compare the modulation bandwidth vs. current density for LEDs on nonpolar (101¯0), semipolar (202¯1¯), and polar 0001 orientations. In agreement with wavefunction overlap considerations, the experimental results indicate a higher modulation bandwidth for the nonpolar and semipolar LEDs, especially at relatively low current densities. At 500 A/cm2, the nonpolar LED has a 3 dB bandwidth of ∼1 GHz, while the semipolar and polar LEDs exhibit bandwidths of 260 MHz and 75 MHz, respectively. A lower carrier density for a given current density is extracted from the RF measurements for the nonpolar and semipolar LEDs, consistent with the higher wavefunction overlaps in these orientations. At large current densities, the bandwidth of the polar LED approaches that of the nonpolar and semipolar LEDs due to coulomb screening of the polarization field. The results support using nonpolar and semipolar orientations to achieve high-speed LEDs at low current densities.

Strain-induced indium clustering in non-polar a-plane InGaN quantum wells

In conventional light-emitting diodes the epitaxial strain and related piezoelectric polarization arising along the polar [0001] growth direction of the InGaN/GaN quantum wells (QWs) induce internal fields which adversely affect the radiative recombination of electron-hole pairs therein. Growing the quantum wells along a nonpolar orientation can, in principle, avoid this problem but seems to face with another problem associated with indium clustering. In this study, we present experimental evidence that supports the inhomogeneous distribution of indium in non-polar a-plane InGaN QWs by using dark-field inline electron holography as well as atom probe tomography measurements and discuss the possible origin by density functional theory calculation. A model non-polar a-plane QW structure with 10 nm-thick In0.1Ga0.9N double QWs was investigated and compared with the polar c-plane QWs with the same QW structure. Unlike the random distribution in the polar QWs, the indium atoms in the non-polar QW exhibit inhomogeneous distribution and show a tendency of periodic clustering. We suggest the dipole interaction energy and the strain energy associated with indium substitution could have a substantial influence on the local composition of strained InGaN QWs and, particularly, triggers In clustering in the non-polar a-plane QW structure. Accompanying phase field modeling rationalizes that In clustering can also modify the in-plane polarization through piezoelectric effects, preventing the electrostatic potential from diverging along the in-plane polar direction.

Optimizing GaInN/GaN light-emitting diode structures under piezoelectric polarization

We model and optimize various light emitting diode structures under bias voltage to maximize emission efficiency with particular respect to piezoelectric polarization. We compare polar and non-polar structures, namely, wurtzite c-plane, a-plane, (11–22) semi-polar, and (001) cubic crystal orientations in self-consistent Schrödinger-Poisson and drift-diffusion models. We consider both structures strained to a GaN pn-junction and strain-reduced systems based on GaInN templates. In light of numerous experimental findings of the actual electric field strength, we find it necessary to reduce the piezoelectric coefficients over those commonly cited. A weaker variation with composition or wavelength is the consequence. For the non-polar and cubic systems, we find a 22% increase of the electron-hole overlap and an 18% increase for the c-plane strain-reduced system at an InN fraction of x = 0.30 when compared to standard c-plane structures. For the green and longer wavelength range, we find that strain-reduced and cubic GaN systems should hold particular promise for higher radiative efficiency.

Growth conditions of semi and non-polar GaN on Si with Er2O3 buffer layer

The GaN was grown on Si(100) with Er2O3(110) buffer by metal organic chemical vapor deposition (MOCVD). The results showed the polycrystalline nature of the layers with dominant non-polar (11–20) and semi-polar (10–13) orientations. GaN was formed in a two step process regime: low temperature growth was followed by high temperature growth regime. At a low temperature GaN tends to crystalize with dominant non-polar (11–20) orientation, while high temperature leads to preferential semi-polar (10–13) orientation growth. Additionally, the effects of parameters such as growth temperature, V/III-ratio and type of carrier gases on structural, morphological and optical properties of GaN was discussed in the current work.

Atomistic modeling of nonpolar m-plane InGaN disk-in-wire light emitters

InGaN heterostructures, when grown along the polar c-plane orientation, are prone to large internal polarization fields, which significantly affect their electronic bandstructure and optical properties and result in poor quantum efficiency. In this regard, devices grown in nonpolar crystal orientations (with zero spontaneous polarization) are promising and were reported to exhibit higher efficiency. In this paper, we first present the numerical implementation of wurtzite nonpolar m-plane crystallographic orientation within a 10-band $$sp^{3}s^{*}$$ (with spin) tight-binding formalism as available in the atomistic three-dimensional Nanoelectronic Modeling (NEMO 3-D) toolkit. In conjunction with a TCAD simulator, we then evaluate and compare the performance of $$\hbox {In}_{0.25}\hbox {Ga}_{0.75}\hbox {N/GaN}$$ disk-in-wire light-emitting diodes in c-plane and m-plane crystallographic orientations in terms of polarization fields, electronic bandstructure, interband optical transition rates, and internal quantum efficiency (IQE). In contrast to bulk and quantum well structures m-plane, where the net polarization potential is ideally zero, the disk-in-wire configuration considered in this study exhibits a small internal potential. Overall, the m-plane structure, as compared to the c-plane counterpart, offers higher spontaneous emission rate and IQE as well as an improved efficiency droop characteristic.

Thin-Wall GaN/InAlN Multiple Quantum Well Tubes.

Thin-wall tubes composed of nitride semiconductors (III-N compounds) based on GaN/InAlN multiple quantum wells (MQWs) are fabricated by metal-organic vapor-phase epitaxy in a simple and full III-N approach. The synthesis of such MQW-tubes is based on the growth of N-polar c-axis vertical GaN wires surrounded by a core-shell MQW heterostructure followed by in situ selective etching using controlled H2/NH3 annealing at 1010 °C to remove the inner GaN wire part. After this process, well-defined MQW-based tubes having nonpolar m-plane orientation exhibit UV light near 330 nm up to room temperature, consistent with the emission of GaN/InAlN MQWs. Partially etched tubes reveal a quantum-dotlike signature originating from nanosized GaN residuals present inside the tubes. The possibility to fabricate in a simple way thin-wall III-N tubes composed of an embedded MQW-based active region offering controllable optical emission properties constitutes an important step forward to develop new nitride devices such as emitters, detectors or sensors based on tubelike nanostructures.