Plane AlGaN Research Articles

Improved characteristics of (11 [formula omitted]) plane AlGaN films grown on SiNx interlayer

SiNx interlayer was introduced in the epitaxial process of (11 2‾2) AlGaN film, and the influences of SiNx on the properties of (11 2‾2) AlGaN were characterized. It was revealed that the morphologic properties and crystal quality of (11 2‾2) AlGaN could be refined remarkably by optimizing SiNx growth time. Especially, a low root mean square value of 1.02 nm was obtained for S3 with a SiNx growth time of 10 min, which was 56.7 % less than S0 that grown without SiNx. Meanwhile, compared with S0, the full width at half maximum values of X-ray rocking curves for S3 were reduced by 39.6 % along [11 2‾3‾] direction and 41.2 % along [1 1‾00] direction. Besides, the background electron concentration and basal stacking faults related emission of (11 2‾2) AlGaN could also be suppressed remarkably by optimizing SiNx growth time to 10 min. These improvements could be originated from the formation of SiNx islands, leading to the lateral growth of AlGaN overlayer, the relaxation of strain in the AlGaN, and the annihilation of dislocations.

Influences of nitridation treatment on the properties of semi-polar (11 [formula omitted]) plane AlGaN films

The characteristics of the semi-polar (11 2‾ 2) plane Al0.34Ga0.66N films grown with various nitridation time for m-plane substrate were investigated. The characterization results demonstrated that the surface flatness, crystalline quality as well as the PL full width at half maximum values were sensitive to the nitridation time, indicating that nitridation time is a key factor to achieve (11 2‾ 2) plane AlGaN films with high quality. Meanwhile, the background electron concentration in the epi-layer reduced by nearly two orders of magnitude via optimizing the nitridation time. These results made remarkably positive contributions to obtaining (112‾ 2)-orientated p-AlGaN films with high concentration, which is of great importance in fabricating high efficiency (112‾ 2)-orientated AlGaN-based light emitting diodes.

Optical properties of quasi-ordered [formula omitted] AlGaN multi-quantum-well nanorod arrays

Quasi-ordered semi-polar 112̅2 plane AlGaN multiple-quantum-well (MQW) nanorod (NR) arrays with a period of 400 nm were successfully fabricated by a self-assembly technique using polystyrene spheres. The diameter and height of the NRs were about 360 and 600 nm, respectively. The photoluminescence (PL) peak wavelengths of both NR and planar MQWs were located at 266 nm at room temperature, demonstrating that the quantum-confined Stark effect was negligible in the semi-polar AlGaN MQWs. The PL integral intensity of the MQW NR arrays was enhanced by 1.5 times compared to that of planar MQWs. Moreover, the degree of polarization was increased from 15.9% to 26.2% when fabricating the NR arrays, demonstrating enhanced polarized emission. The finite-difference time-domain method was used to explain the enhancement of PL intensity, which was mainly due to the modified light extraction by the quasi-ordered NR arrays.

Effects of indium surfactant on growth and characteristics of (112¯2) plane AlGaN-based multiple quantum wells

High quality semi-polar (112¯2) plane AlGaN-based multiple quantum wells (MQWs) were successfully grown on (101¯0) m-plane sapphire substrates with metal-organic chemical vapor deposition (MOCVD) technology and the effects of indium (In) surfactant on the structural and optical properties of the AlGaN-based MQWs were investigated intensively. The characterization results revealed that the surface morphology as well as the crystalline quality for the semi-polar (112¯2) plane AlGaN MQWs could be improved remarkably by adopting In as surfactant during the MOCVD growth process. Furthermore, the integrated MQWs-related excition emission peak intensity and the radiative recombination probabilities in MQWs could be increased as well with the help of In-surfactant, resulting an enhanced internal quantum efficiency.

Effects of Mg-doping on characteristics of semi-polar [formula omitted] plane p-AlGaN films

The effects of Mg-doping on the characteristics of semi-polar (112¯2) plane Al0.15Ga0.85N films grown on (101¯0) m-plane sapphire substrates with metal-organic chemical vapor deposition (MOCVD) technique were investigated intensively and systematically. The characterization results showed that the crystalline quality of the (112¯2) plane AlGaN films could be improved by optimizing the Mg-delta-doping process. Whereas, the surface morphology for the samples was monotonously degraded with increasing the Mg-doping level. Meanwhile, a hole concentration as high as 5.4×1017cm−3 were achieved by optimizing the Mg-doping level. Furthermore, the luminescence mechanism of the samples was investigated by photoluminescence spectra at room temperature.

Indium-surfactant-assisted epitaxial growth of semi-polar $$\left(11\overline{2}2\right)$$ 11 2 ¯ 2 plane Al0.42Ga0.58N films

The semi-polar $$\left(11\overline{2}2\right)$$ plane Al0.42Ga0.58N films were successfully grown on $$\left(10\overline{1}0\right)$$ -oriented m-plane sapphire substrates for the first time with an indium (In)-surfactant-assisted metal–organic chemical vapor deposition (MOCVD) technology. The crystal orientation, surface morphology, and electrical properties of the grown semi-polar $$\left(11\overline{2}2\right)$$ plane AlGaN epi-layers were characterized with high-resolution X-ray diffraction (HR-XRD), atomic force microscopy (AFM), and Hall effect measurements, respectively. The XRD scanning results showed that crystalline quality for the semi-polar $$\left(11\overline{2}2\right)$$ plane AlGaN epi-layer was improved with In-surfactant. The AFM results demonstrated that the root mean square value of the semi-polar AlGaN epi-layer samples decreased with increasing the TMIn mole flow rate. Furthermore, the native electron concentration of the unintentionally doped semi-polar $$\left(11\overline{2}2\right)$$ plane AlGaN epi-layers was decreased from 2.66 × 1017 to 2.97 × 1016 cm−3 due to the significant decrease in nitrogen vacancies (V N) with indium-surfactant-assisted growth process.

Inductively coupled plasma–reactive ion etching of c- and a-plane AlGaN over the entire Al composition range: Effect of BCl3 pretreatment in Cl2/Ar plasma chemistry

Inductively coupled plasma (ICP)–reactive ion etching (RIE) patterning is a standard processing step for UV and optical photonic devices based on III-nitride materials. There is little research on ICP-RIE of high Al-content AlGaN alloys and for nonpolar nitride orientations. The authors present a comprehensive study of the ICP-RIE of c- and a-plane AlGaN in Cl2/Ar plasma over the entire Al composition range. The authors find that the etch rate decreases in general with increasing Al content, with different behavior for c- and a-plane AlGaN. They also study the effect of BCl3 deoxidizing plasma pretreatment. An ICP deoxidizing BCl3 plasma with the addition of argon is more efficient in removal of surface oxides from AlxGa1−xN than RIE alone. These experiments show that AlxGa1−xN etching is affected by the higher binding energy of AlN and the higher affinity of oxygen to aluminum compared to gallium, with oxides on a-plane AlGaN more difficult to etch as compared to oxides on c-plane AlGaN, specifically for high Al composition materials. The authors achieve reasonably high etch rate (∼350 nm/min) for high Al-content materials with a smooth surface morphology at a low DC bias of ∼−45 VDC.

Carbon‐doped p‐type (0001) plane AlGaN (Al = 6–55%) with high hole density

AbstractIn this paper, promising experimental results for the p‐type electrical properties of carbon‐doped (C‐doped) AlGaN are discussed. P‐type conductivity was experimentally achieved in C‐doped (0001) plane AlGaN layers with from a small amount to 55% solid Al composition, but not in (0001) plane GaN. The maximum free hole density (determined by van der Pauw geometry‐Hall effect measurement) achieved for an AlGaN layer with 10% solid Al composition was p = 3.2 × 1018 cm−3. The maximum net ionized acceptor densities (NIAD), $N_{{\rm A}}^{- } - N_{{\rm D}}^{ + } $, which were determined by capacitance–voltage measurement, for AlGaN with 6, 10, 27, and 55% solid Al compositions, were all in the range of (6–7) × 1018 cm−3. Moreover, the electrical activity of the carbon acceptors was estimated to be 55–71% from the NIAD and secondary‐ion microprobe mass spectrometry analysis data on the carbon concentration. A p–n junction was also fabricated using the C‐doped p‐type AlGaN.

MOVPE growth and characterization of a ‐plane AlGaN over the entire composition range

AbstractWe report the metal organic vapor phase epitaxy (MOVPE) growth and characterization of non‐polar (11$ \bar 2 $0) a ‐plane Alx Ga1–xN on (1$ \bar 1 $02) r ‐plane sapphire substrates over the entire composition range. Alx Ga1–xN samples with ∼0.8 μm thick layers and with x = 0, 0.18, 0.38, 0.46, 0.66, and 1.0 have been grown on r ‐plane sapphire substrates. The layer quality can be improved by using a 3‐stage AlN nucleation layer and appropriate V/III ratio switching following nucleation. All a ‐plane AlGaN epilayers show an anisotropic in‐plane mosaicity, strongly influenced by Al incorporation and growth conditions. Careful lattice parameter measurements show anisotropic in‐plane strain that results in an orthorhombic distortion of the hexagonal unit cell, making Al composition determination from X‐ray diffraction difficult. In general lower Al incorporation is seen in a ‐plane epilayers compared to c ‐plane samples grown under the same conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A ‐plane AlN and AlGaN growth on r ‐plane sapphire by MOVPE

AbstractThe growth of a‐plane (11‐20) AlN and AlGaN on r‐plane (1‐102) sapphire has been investigated with the aim of application to LEDs and LDs in the deep ultra‐violet region. a‐plane AlN and AlGaN were grown on r‐plane sapphire by low‐pressure metalorganic vapor phase epitaxy (LP‐MOVPE). The crystalline quality and surface morphology of a‐plane AlN were optimized at a growth temperature of 1250 °C with the off‐angle of r‐plane sapphire between ‐1° and +1°, and a‐plane AlGaN grown on the AlN layer using ‐0.45°‐off r‐plane sapphire as a substrate exhibited high crystalline quality. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Non-catalyst growth and characterization ofa-plane AlGaN nanorods

We report on growth of Al 0.22 Ga 0.78 N/Al 0.06 Ga 0.94 N nanorods over a-plane GaN template using low pressure metal-organic chemical vapor deposition. Nanorods with average diameter of 100 nm were up to 30 μm long. They grew preferentially along the crystal direction and possessed excellent optical and mechanical properties. It was shown using monochromatic cathodoluminescence that nanorods emit light both at 320 nm and 350 nm over entire length proving uniform coating of the Al 0.06 Ga 0.94 N rod core by an Al 0.22 Ga 0.78 N shield. The elastic modulus of nanorod material was found to be 185 GPa.