InAlGaN Layers Research Articles

Growth of ultrathin barrier InAlGaN/GaN heterostructures with superior properties using sputtered AlN/sapphire templates and optimized group-III injection rate by metalorganic chemical vapor phase deposition

In this paper, we investigate the influence of group-III precursor injection rate on the material and electrical properties of InAlGaN/GaN heterostructures grown by Metalorganic Chemical Vapor Phase Deposition. It is demonstrated that high-quality GaN layers can be achieved by using the sputtered AlN/sapphire templates. During the barrier layer growth, the injection rate of the Trimethylindium plays an important role in the amount of Ga incorporation into the InAlGaN layer, while the variation of Trimethylaluminum has less impact. High mobility of 1800 cm2/(V·s) and high carrier electron density with an ultrathin of 3 nm thickness InAlGaN barrier layer simultaneously maintaining high crystallinity and smooth surface of InAlGaN barrier layer is achieved with sputtered AlN/sapphire templates and optimized group-III injection rate.

E-mode All-GaN-Integrated cascode MISHEMT with GaN/InAlGaN/GaN backbarrier for high power switching performance: Simulation study

In this work, simulation-based research work based on a novel All-GaN-Integrated Cascode (AGC) MISHEMT with quaternary layer InyAlxGa1-x-yN as backbarrier has been investigated. The AGC-MISHEMT device consists of series combination of enhancement mode (recessed gate MISHEMT) and depletion-mode (MIS-gate) GaN devices with GaN/InAlGaN/GaN sandwich back barrier (SW-BB). TCAD simulations indicate that AGC-MISHEMTs with sandwich back barrier (SW-BB) exhibits simultaneous improvement in terms of drain current density (267 ​mA/mm), high ION/IOFF ratio (108), transconductance-peak (191 ​mS/mm) and breakdown voltage (371 ​V) as compared to AGC-MISHEMT with GaN buffer. The impact of varying mole fractions (x, y), thickness and position of InyAlxGa1-x-yN layer on breakdown voltage has also been examined. Improvement in drain current density up to 40% has been accomplished with increased gate oxide thickness under gate 2 (depletion-mode device) for AGC-MISHEMT with SW-BB. Besides, power switching performance has been compared for AGC-MISHEMT with SW-BB to that of AGC-MISHEMT with GaN buffer and Recessed Single Gate (RSG) MISHEMT for inductive load circuit. Significant reduction in power switching losses (i.e. 43% during turn-ON time and 87% during turn-OFF time) has been observed for AGC-MISHEMT with SW-BB as compared to RSG-MISHEMT. In addition, introduction of quaternary InAlGaN layer in backbarrier for AGC-MISHEMT also results in considerable degradation (∼89%) in power loss when input gate is in OFF-state due to improved ION/IOFF ratio in contrast with recessed single gate device.

Optimization for the growth condition of in situ SiN x cap layer on ultrathin barrier InAlGaN/GaN heterostructures by metal-organic chemical vapor deposition

We investigate the dependence of material and electrical properties on the growth temperature of in situ SiN x on InAlGaN/GaN heterostructures grown by metal-organic chemical vapor deposition. Degradation of the interface between SiN x and InAlGaN layer was observed when growth temperature is below 900 °C or above 1100 °C. With the optimized SiN x growth temperature, the high-quality SiN x and low interface trap density can be realized. Thus, the double-sweep capacitance–voltage measurement showed a sharp transition from charge accumulation to depletion with low hysteresis of 0.09 V. A small threshold-voltage shift after gate bias stress (1001 s) was also characterized by I–V measurement.

Enhancement of electron transport properties of InAlGaN/AlN/GaN HEMTs on silicon substrate with GaN insertion layer

InAlGaN/AlN/GaN high electron mobility transistors (HEMTs) on a silicon substrate with high electron mobility is demonstrated for the first time. The InAlGaN/AlN/GaN heterostructures has a high electron mobility of 1540 cm2 V−1 s−1 and low sheet resistance of 228.2 Ω sq−1 by inserting a thin GaN interlayer (IL) between InAlGaN and AlN layers. The experimental results demonstrate that an optimized GaN IL contributes to a better atomic arrangement of the InAlGaN barrier layer in the InAlGaN/GaN HEMTs and results in better electron transport properties for the device. The InAlGaN/GaN device with 170 nm gate and 2 μm source-to-drain distance shows a high maximum current density (Imax) of 1490 mA mm−1 and high transconductance (gm) of 401 mS mm−1. Such results demonstrate the potential of adopting InAlGaN/GaN heterostructure on silicon for low cost mm-wave applications in the future.

Structural and electrical properties analysis of InAlGaN/GaN heterostructures grown at elevated temperatures by MOCVD

We report the effects of the growth temperature on the structural and electrical properties of the InAlGaN/GaN heterostructures grown on c-plane sapphire substrates. X-ray Photoelectron Spectroscopy and Atomic Force Microscopy measurements results indicate that the InAlGaN layer properties is strongly dependent on the growth temperature. It is observed that the Gallium incorporation increases with the increase of the growth temperature. Meanwhile, the surface roughness decreases from 0.49 nm to 0.34 nm with the increase of growth temperature. The variation of structural properties, composition and surface morphology influences the transport properties of the InAlGaN/GaN heterostructures. High 2DEG electron density, low sheet resistance and good C-V response with a steep slope for InAlGaN/GaN HEMT were achieved at an optimized growth temperature window between 900 °C and 950 °C.

The structure of InAlGaN layers grown by metal organic vapour phase epitaxy: effects of threading dislocations and inversion domains from the GaN template.

Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer surface, and this is related to the change in growth kinetics on top and at the immediate surroundings of the ID.

Impact of Gate–Drain Spacing on Low-Frequency Noise Performance of <italic>In Situ</italic> SiN Passivated InAlGaN/GaN MIS-HEMTs

In this paper we investigated the gate–drain access region spacing ( $L_{\mathrm {GD}})$ effect on electrical and noise performance of InAlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) using in situ SiN cap layer as gate insulator. Different $L_{\mathrm {GD}}$ of InAlGaN/GaN MIS-HEMTs using sub-10 nm barrier layer are studied. Low-frequency noise measurements have been carried out for the first time in order to analyze the impact of the gate–drain spacing on the electrical characteristics. The noise of the channel under the gate has been identified as the dominant channel noise source for $L_{\mathrm {GD}} . Finally, the calculated Hooge parameter ( $\alpha _{H})$ is equal to $3.1\times 10^{-4}$ . It reflects the high material quality while using sub-10 nm InAlGaN layer, which is promising for high-frequency applications.

A Model of Radiative Recombination in (In,Al,Ga)N/GaN Structures with Significant Potential Fluctuations

The potential fluctuations in III-nitride quantum wells lead to many effects like emission broadening and S-shape energy vs. temperature dependence. The best description of the energy dependence comes from calculations based on Gaussian density of states. However, in most of the published reports, changes of carrier lifetime with energy and temperature are not taken into account. Since experimental evidence shows that lifetime significantly depends on energy and temperature, here we propose a model that describes two basic parameters of luminescence: lifetime of carries and emission energy as a function of temperature in the case of quantum wells and layers that are characterized by potential fluctuations. Comparison of the measured energy and lifetime dependences on temperature in specially grown InGaN/GaN quantum wells and InAlGaN layer shows very good agreement with the proposed theoretical approach.

Fabrication of GaN-Based Heterostructures with an InAlGaN/AlGaN Composite Barrier**Supported by the National Science and Technology Major Project under Grant No 2013ZX02308-002, and the National Natural Science Foundation of China under Grant Nos 11435010, 61474086 and 61334002.

GaN-based heterostructures with an InAlGaN/AlGaN composite barrier on sapphire (0001) substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAlGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostructures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlGaN quaternary layer is nearly lattice-matched to the GaN channel. Capacitance–voltage results show that there is no parasitic channel formed between the InAlGaN layer and the AlGaN layer. Compared with the InAlGaN/GaN heterostructure, the electrical properties of the InAlGaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V · s, 1.44 × 1013 cm−2 and as low as 201.1 ω/sq, respectively.

Inline electron holography and VEELS for the measurement of strain in ternary and quaternary (In,Al,Ga)N alloyed thin films and its effect on bandgap energy.

We present the use of (1) dark-field inline electron holography for measuring the structural strain, and indirectly obtaining the composition, in a wurtzite, 4-nm-thick InAlGaN epilayer on a AlN/GaN/AlN/GaN multinano-layer heterosystem, and (2) valence electron energy-loss spectroscopy to study the bandgap value of five different, also hexagonal, 20-50-nm-thick InAlGaN layers. The measured strain values were almost identical to the ones obtained by other techniques for similarly grown materials. We found that the biaxial strain in the III-N alloys lowers the bandgap energy as compared to the value calculated with different known expressions and bowing parameters for unstrained layers. By contrast, calculated and experimental values agreed in the case of lattice-matched (almost unstrained) heterostructures.

Improved light-output power of InGaN-based multiple-quantum-well light-emitting diodes by GaN/InAlGaN/GaN multi-barrier

InGaN/GaN-based LED structures were grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). We inserted thin InAlGaN layer into the GaN barrier in the form of multi-layer barrier (MLB) and investigated the effect of MLB on the performance of InGaN/GaN-based LEDs. MLB consisted of GaN/InAlGaN/GaN layers by replacing conventional GaN single barrier. Lateral LED chips (375 μm × 435 μm) were fabricated and also evaluated by light–current–voltage (L–I–V) measurements. The effect of MLB on surface morphologies of MLB was investigated by atomic force microscopy (AFM). For LED with MLB, efficiency and optical power were improved significantly although there was still efficiency degradation with injection current. This indicates that InAlGaN layer in MLB was helpful to reduce the electron overflow. From photoluminescence (PL) and atomic force microscopy (AFM) measurement, it was revealed that the adoption of MLB for LED was also beneficial to improve the crystal quality of MQWs.

Structural and optical properties of Ga auto-incorporated InAlN epilayers

InAlN epilayers deposited on thick GaN buffer layers grown by metalorganic chemical vapour deposition (MOCVD) revealed an auto-incorporation of Ga when analysed by wavelength dispersive x-ray (WDX) spectroscopy and Rutherford backscattering spectrometry (RBS). Samples were grown under similar conditions with the change in reactor flow rate resulting in varying Ga contents of 12–24%. The increase in flow rate from 8000 to 24000sccm suppressed the Ga auto-incorporation which suggests that the likely cause is from residual Ga left behind from previous growth runs. The luminescence properties of the resultant InAlGaN layers were investigated using cathodoluminescence (CL) measurements.

Characterization of temperature-dependent photoluminescence properties of InAlGaN quaternary alloys

Abstract Samples containing thin InAlGaN layers grown on c -Al 2 O 3 substrates by metalorganic chemical vapor deposition have been studied experimentally and theoretically with the help of photoluminescence measurements between 10 and 300 K. From the analysis of the temperature dependence photoluminescence spectra with the modified Bose–Einstein equation, the localization energy of excitons was estimated successfully and the value is found out to be well correlated to the strength of the electron/exciton-phonon interaction as well as the stress observed in the X-ray diffraction spectra. These results are also confirmed that the c -axis length decreases as the increasing Al/In ratio corresponding to the decreased compressive stress which would be attributed to the increased tensile stress formed by Al atoms incorporated.

Evaluation of interpolations of InN, AlN and GaN lattice and elastic constants for their ternary and quaternary alloys

Structural and compositional data were collected for several high-quality strained InGaN, InAlN, AlGaN and InAlGaN layers with various compositions. Based on these results, the InN/AlN/GaN molar fractions of every film were indirectly estimated by the application of Vegard's law (Vegard 1921 Z. Phys. 5 17) to lattice and elastic constants of the binaries and by an alternative approach proposed by (Williams et al 1978 J. Electron. Mater. 7 639) (even considering possible mistakes in its application). True compositions were independently assessed by x-ray spectroscopy or Rutherford backscattering spectrometry. The results of both interpolation models are highlighted in utilizable contour and surface ternary plots of lattice constants and biaxial strain relaxation coefficients calculated for the whole compositional range. Calculated compositions from Vegard's law best fit the measured values. Finally, it is geometrically demonstrated that there are wrong assumptions in the Williams et al model, so that Vegard's law should only be used to successfully determine the compositions of ternary and quaternary III-N nitrides.

222–282 nm AlGaN and InAlGaN‐based deep‐UV LEDs fabricated on high‐quality AlN on sapphire

AbstractWe demonstrate 222–282 nm AlGaN and InAlGaN‐based deep ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on low threading dislocation density (TDD) AlN template. Low TDD AlN templates were realized by using ammonia (NH3) pulse‐flow multilayer (ML) growth technique. The edge‐ and screw‐type dislocation densities of AlN layer were reduced to 7.5 × 108 and 3.8 × 107, respectively. Single‐peaked electroluminescence (EL) were obtained for 222– 273 nm AlGaN multi quantum well (MQW) DUV‐LEDs. We obtained the maximum output power of 1.1 mW and 4.0 mW for the AlGaN‐QW LEDs with wavelengths of 241 nm, 256 nm, respectively, under room temperature (RT) CW operations. The maximum output power of 227 nm and 222 nm AlGaN‐QW were 0.15 mW and 0.014 mW, respectively, under RT pulsed operation. The maximum external quantum efficiency (EQE) of the 227 nm and 250 nm AlGaN LEDs were 0.2% and 0.43%, respectively. We also fabricated 280 nm band quaternary InAlGaN‐MQW DUV‐LEDs with n‐type and p‐type InAlGaN layers on ML‐AlN templates. We demonstrated extremely high internal quantum efficiency (IQE) of 284 nm InAlGaN‐QW emission, which was confirmed by the fact that the ratio of the integrated intensity of the RT‐PL against the 77 K‐PL was 86%. The maximum output power and EQE of the 282 nm InAlGaN LED were 10.6 mW and 1.2%, respectively, under RT CW operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Extremely high efficiency 280 nm‐band emission from quaternary InAlGaN quantum wells realized by controlling Si‐doped layers

AbstractQuaternary InAlGaN alloys are attracting much attention as candidate materials for realizing deep ultraviolet (DUV) light‐emitting diodes (LEDs). In this study, we investigated the effect of Si‐doping in the quaternary InAlGaN quantum well (QW) emitting region for obtaining a high efficiency DUV emission. Quaternary InAlGaN multi (M)‐QWs with Si‐doped InAlGaN buffer and barrier layers were grown on sapphire (0001) / AlN / AlGaN template by low‐pressure metal‐organic chemical‐vapor deposition (LP‐MOCVD). We found that the surface roughness of InAlGaN layer was significantly improved by introducing the light‐doping of Si. The oxygen impurity concentration in the quaternary InAlGaN layer was significantly reduced by the small amount of Si‐doping. We also revealed that the emission efficiency of the InAlGaN QW was markedly improved by inserting thin (3‐nm‐thick) undoped InAlGaN interlayer between n‐AlGaN buffer and n‐InAlGaN layers. At last, we demonstrated extremely high intensity PL emission from 280 nm‐band InAlGaN QWs at room temperature (RT). The ratio of the integrated intensity of the RT‐PL against the 77 K‐PL was 86%. This result suggests that the internal quantum efficiency (IQE) of the InAlGaN‐QW is considerably high. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High‐resolution Rutherford backscattering spectrometry for InAlGaN/AlGaN single quantum well structure

AbstractInAlGaN/AlGaN single quantum well (SQW) structure has been studied by means of high‐resolution Rutherford backscattering spectrometry (HRBS). The HRBS spectrum of a SQW structure was clearly observed. The composition of each layer was estimated to be In0.02Al0.17Ga0.81N/Al0.28Ga0.72N from the HRBS measurement. The channeling measurement shows the high degree of the crystalline perfection that can be achieved in such epitaxial layers from the minimum yield of 3.2% in the direction of the <11–23> axis. The channeling measurement also shows atomic disorder differences between InAlGaN epitaxial layer and AlGaN epitaxial layer. Furthermore Al, Ga and In minimum yields in the InAlGaN layer were estimated to be χmin(Ga) = 4.9%, χmin(Al) = 9.4% and χmin(In) = 6.6%, respectively. Larger normalized yield of Al than those of Ga and In in the InAlGaN layer indicates that Al atomic disorder becomes larger to compensate the compressive stress of Ga and In. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

340 nm‐band high‐power InAlGaN quantum well ultraviolet light‐emitting diode using p‐type InAlGaN layers

AbstractIn order to achieve high‐efficiency ultraviolet (UV) light‐emitting diodes (LEDs), p‐type layers with sufficient hole concentration is quite important to suppress the electron overflow. We introduced Mg‐doped InAlGaN for p‐type layers of the UV‐LEDs for the purpose of obtaining higher hole concentration, and achieved high power CW operations of the UV‐LEDs. 340 nm‐band InAlGaN‐based multi‐quantum‐well (MQWs) UV‐LEDs with Mg‐doped InAlGaN electron‐blocking layer (EBL) and Mg‐doped InAlGaN layers were grown on sapphire substrates by metal‐organic chemical vapor deposition (MOCVD). The output power of UV‐LED with p‐InAlGaN layers was approximately 4.7 times larger than that with p‐AlGaN layers. Maximum output power and the external quantum efficiency (EQE) of the LED with p‐InAlGaN layers were 8.4 mW and 0.9%, respectively, at emission wavelength of 346 nm under room temperature (RT) CW operation. From these results, p‐InAlGaN is shown to be useful for the realization of high‐efficiency UV‐LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Realization of 340-nm-Band High-Output-Power (>7 mW) InAlGaN Quantum Well Ultraviolet Light-Emitting Diode with p-Type InAlGaN

We have demonstrated 340-nm-band high-output-power InAlGaN quantum well (QW) ultraviolet (UV) light-emitting diodes (LEDs) under room temperature (RT) continuous wave (CW) operation, which were deposited on sapphire (0001) substrates by low-pressure metal–organic chemical vapor deposition (LP-MOCVD). The high-output-power UV LEDs were achieved by introducing p-type InAlGaN layers in order to obtain a high hole concentration and by optimizing the band lineup to suppress electron overflow. The output power of a UV-LED with p-InAlGaN layers was about 4.7 times larger than that of an equivalent structure containing p-AlGaN. We obtained a significant increase in output power by controlling the barrier height of the electron-blocking layer (EBL) and the depth of the quantum wells. We also obtained a marked increase in UV output power by introducing a low-threading-dislocation-density (TDD) AlN buffer layer. The maximum output power and external quantum efficiency (EQE) of LEDs containing p-InAlGaN layers were 8.4 mW and 0.9%, respectively, at an emission wavelength of 346 nm under room temperature (RT) CW operation.

Realization of 340nm-Band High-Power UV-LED Using P-Type Inalgan

High output power 340 nm-band InAlGaN-based multi-quantum-well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) were achieved by using p-type InAlGaN layers. The output power of a UV-LED with p-type InAlGaN layers was approximately 4.7 times larger than that achieved with p-type AlGaN layers. We obtained an output power of 8.4mW from a 346 nm InAlGaN-QW LED by optimizing the band line-up to suppress electron overflow and by reducing the threading dislocation density (TDD) of the AlN/AlGaN template.