Energy Band/Lattice Mismatch Engineering in Quaternary AlInGaN/GaN Heterostructure (original) (raw)
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Lattice and energy band engineering in AlInGaN/GaN heterostructures
Applied Physics Letters, 2000
We report on structural, optical, and electrical properties of Al x In y Ga 1ϪxϪy NGaN heterostructures grown on sapphire and 6H-SiC substrates. Our results demonstrate that incorporation of In reduces the lattice mismatch, ⌬a, between AlInGaN and GaN, and that an In to Al ratio of close to 1:5 results in nearly strain-free heterostructures. The observed reduction in band gap, ⌬E g , determined from photoluminescence measurements, is more than 1.5 times higher than estimated from the linear dependencies of ⌬a and ⌬E g on the In molar fraction. The incorporation of In and resulting changes in the built-in strain in AlInGaN/GaN heterostructures strongly affect the transport properties of the two-dimensional electron gas at the heterointerface. The obtained results demonstrate the potential of strain energy band engineering for GaN-based electronic applications. © 2000 American Institute of Physics. ͓S0003-6951͑00͒03909-7͔
Journal of Applied Physics, 2009
The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/ AlN/GaN two-dimensional electron gas ͑2DEG͒ heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm 2 / V s along with 8.44ϫ 10 12 cm −2 electron density, which resulted in a two-dimensional sheet resistance of 435 ⍀ / ᮀ for the Al 0.2 Ga 0.8 N / AlN/ GaN heterostructure. The sample designed with an Al 0.88 In 0.12 N barrier exhibited very high sheet electron density of 4.23ϫ 10 13 cm −2 with a corresponding electron mobility of 812 cm 2 / V s at room temperature. A record two-dimensional sheet resistance of 182 ⍀ / ᮀ was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al 0.88 In 0.12 N / AlN/ GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al 0.88 In 0.12 N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors ͑HEMTs͒, after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs.
New Journal of …, 2009
The scattering mechanisms governing the transport properties of high mobility AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures with various AIN spacer layer thicknesses from zero to 2 nm were presented. The major scattering processes including acoustic and optical phonons, ionized impurity, interface roughness, dislocation and alloy disorder were applied to the temperature-dependent mobility data. It was found that scattering due mainly to alloy disorder limits the electron mobility for samples having spacer layer thicknesses up to 0.3 nm. On the other hand, alloy scattering is greatly reduced as the AlN spacer layer thickness increases further, and hence the combination of acoustic, optical and interface roughness become operative with different degrees of effectiveness over different temperature ranges. The room-temperature electron mobility was observed to increase gradually as the AlN spacer layer increases. A peak electron mobility of 1630 cm 2 V −1 s −1 was realized for the sample consisting of a 1 nm AlN spacer layer. Then, 2 the electron mobility decreased for the sample with 2 nm AlN. Moreover, the measured 2DEG densities were also compared with the theoretical predictions, which include both piezoelectric and spontaneous polarization components existing at AlN/GaN interfaces. The experimental sheet carrier densities for all AlInN/AlN/GaN HEMT structures were found to be in excellent agreement with the theoretical predictions when the parasitic (unintentional) GaN layer deposited between AlN and AlInN was taken into account. From these analyses, 1 nm AlN spacer layer thickness is found to be the optimum thickness required for high electron mobility and hence low sheet resistance once the sheet carrier density is increased to the theoretically expected value for the sample without unintentional GaN layer.
Electroreflectance characterization of AlInGaN/GaN high-electron mobility heterostructures
Semiconductor Science and Technology, 2015
Room temperature electroreflectance (ER) spectroscopy has been used to study the fundamental properties of Al x In y Gai .j.^N/AlN/GaN heterostructures under different applied bias. The (OOOl)-oriented heterostructures were grown by metal-organic vapor phase epitaxy on sapphire. The band gap energy of the Al x ln y GcLi_ x _yN layers has been determined from analysis of the ER spectra using Aspnes' model. The obtained values are in good agreement with a nonlinear band gap interpolation equation proposed earlier. Bias-dependent ER allows one to determine the sheet carrier density of the two-dimensional electron gas and the barrier field strength.
physica status solidi (a), 2012
The electron transport properties in Al 0.25 Ga 0.75 N/AlN/GaN/ In x Ga 1Àx N/GaN double heterostructures with various indium compositions and GaN channel thicknesses were investigated. Samples were grown on c-plane sapphire substrates by MOCVD and evaluated using variable temperature Hall effect measurements. In order to understand the observed transport properties, various scattering mechanisms, such as acoustic phonon, optical phonon, interface roughness, background impurity, and alloy disorder, were included in the theoretical model that was applied to the temperature-dependent mobility data. It was found that low temperature (T < 160 K) mobility is limited only by the interface roughness scattering mechanism, while at high temperatures (T > 160 K), optical phonon scattering is the dominant scattering mechanism for AlGaN/ AlN/GaN/InGaN/GaN heterostructures. The higher mobility of the structures with InGaN back barriers was attributed to the large conduction band discontinuity obtained at the channel/ buffer interface, which leads to better electron confinement.
Thin Solid Films, 2014
One AlInN/AlN/GaN single channel heterostructure sample and four AlInN/AlN/GaN/AlN/GaN double channel heterostructure samples with different values of the second GaN layer were studied. The interface profiles, crystalline qualities, surface morphologies, and dislocation densities of the samples were investigated using high resolution transmission electron microscopy, atomic force microscopy, and high-resolution X-ray diffraction. Some of the data provided by these measurements were used as input parameters in the calculation of the scattering mechanisms that govern the transport properties of the studied samples. Experimental transport data were obtained using temperature dependent Hall effect measurements (10-300 K) at low (0.5 T) and high (8 T) magnetic fields to exclude the bulk transport from the two-dimensional one. The effect of the thickness of the second GaN layer inserted between two AlN barrier layers on mobility and carrier concentrations was analyzed and the dominant scattering mechanisms in the low and high temperature regimes were determined. It was found that Hall mobility increases as the thickness of GaN increases until 5 nm at a low temperature where interface roughness scattering is observed as one of the dominant scattering mechanisms. When GaN thicknesses exceed 5 nm, Hall mobility tends to decrease again due to the population of the second channel in which the interface becomes worse compared to the other one. From these analyses, 5 nm GaN layer thicknesses were found to be the optimum thicknesses required for high electron mobility.
BIBECHANA
In spatially confined system such as heterojunction of high and low band gap material, carriers are transferred from higher band gap to the lower band gap. It causes the band bending and the formation of a triangular quantum well at the junction. Such system behaves as quantum-two dimension (Q2D) system because the carriers are free to move on a plane, perpendicular to the junction. Mobility of such quantized system is very high as compare to the bulk system due to the reduction of various scattering mechanisms. GaN is a very useful material. However, a non availability of single crystalline form of GaN and perfectly matched substrates are always problems for GaN. Hence GaN, grown on a substrate such as sapphire is having a very large dislocations at the interface. Such interfacial layer significantly affects the transport parameters of the material, where the transport properties are highly dominated by scattering due to dislocations. The authors have calculated the mobilities of AlGaN/GaN, a heterojunction considering the GaN, grown on Sapphire with reference to the two layer model of Look, in which the 2nd layer is the dislocation layer of GaN and the 1 st layer is the junction of AlGaN/GaN where carriers are in the form of two dimensional electron gas (2D EG). The obtained calculated results are also compared with the experimental results as obtained by Sibel Gokden et al. It is observed that the nature of the curve is found to be in agreement with the experimental curve when the ratio of the thicknesses is taken to be 1:1.