Carrier Concentration In GaN Research Articles

Electrical and optical inhomogeneity in N-face GaN grown by hydride vapor phase epitaxy

A detailed study on electrical and optical inhomogeneity in N-face GaN grown by hydride vapor phase epitaxy is presented. There are two distinctive regions with non-homogeneous electrical and optical properties in N-face of GaN revealed by wet etching, Raman and cathodoluminescence. One region exclusively exhibited stronger donor–acceptor pair emission and higher carrier concentration due to impurity incorporation. A strong red-shift of near band edge emission of ∼24meV was also observed owing to additional carrier concentration. Furthermore, the activation energy difference of the etching process between the two regions is ∼0.12eV. The distinctive etching topography was probably due to the difference of surface potentials related to the level of carrier concentration in GaN.

Interface and transport properties of GaN/graphene junction in GaN-based LEDs

A normalized circular transmission line method pattern with uniform interface area was developed to obtain contact resistances of p-, u-, n-GaN/graphene contacts (p, u and n represent p-type doped, unintentionally doped and n-type doped, respectively) and N-polar u-, n-GaN/graphene contacts in GaN-based LEDs. The resistances of the graphene/GaN contacts were mainly determined by the work function gap and the carrier concentration in GaN. Annealing caused diffusion of metal atoms and significantly influenced the interface transport properties.

Transparency of GaN substrates in the mid‐infrared spectral range

AbstractTransparency of truly bulk GaN substrates obtained by ammonothermal method was measured in the mid infrared spectral range by Fourier spectroscopy. The same measurements were performed for GaN templates grown by meatlorganic vapour phase epitaxy on sapphire and SiC substrates. It has been clearly observed that truly bulk GaN substrates are transparent up to ∼7 µm whereas GaN templates grown on sapphire and SiC are transparent only up to ∼6.5 and ∼5.5 µm, respectively, due to non‐transparency of sapphire and SiC in this spectral range. It has been shown that the transparency “cut off” at ∼7 µm for GaN crystals results from the absorption of light by the second harmonic of optical phonons, which is very significant due to the strong electron‐phonon coupling in this material. Also it has been clearly presented that the absorption “cut‐off” in the infrared spectral region can be easily tuned by increasing of free carrier concentration in GaN. It was observed that the infrared transparency can be shifted from ∼7 to ∼2 µm or even shorter wavelengths when the electron concentration is increased up to ∼1019 cm‐3. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect evolution and accompanied change of electrical properties during the GaN growth by metalorganic chemical vapor deposition

The defect evolution and its correlation with electrical properties of GaN films grown by metalorganic chemical vapor deposition are investigated. It is found that the dislocation density decreases gradually during the growth process, and the dislocation reduction rate in the island coalescence process is especially rapid. The changes in electron mobility of GaN with the increase of growth time are mainly dependent on the dislocations acting as scattering centers. Furthermore, the variation of carrier concentration in GaN may be related with the point defects and their clusters. The quality of GaN could be improved by suitably increasing the film thickness.

Photoelectrochemical reaction and H2 generation at zero bias optimized by carrier concentration of n-type GaN

The authors studied the photoelectrochemical properties dependent on carrier concentration of n-type GaN. The photocurrent at zero bias became the maximum value at the carrier concentration of 1.7x10(17) cm-3. Using the sample optimized carrier concentration, the authors achieved H2 gas generation at a Pt counterelectrode without extra bias for the first time. The authors also discussed the mechanism of the dependence of photocurrent on the carrier concentration of GaN.

Influence of dislocation density on photoluminescence intensity of GaN

The influence of dislocation density on photoluminescence intensity is investigated experimentally and compared to a model. GaN samples were grown by molecular beam epitaxy and metal-organic chemical vapour deposition. Different growth parameters and thicknesses of the layers resulted in different dislocation densities. The threading dislocation density, measured by atomic force microscopy, scanning electron microscopy and X-ray diffraction, covered a range from 5×10 8 to 3×10 10 cm −2. Carrier concentration was measured by capacitance–voltage-, and Hall effect measurements and photoluminescence at 2 K was recorded. A model which accounts for the photoluminescence intensity as a function of dislocation density and carrier concentration in GaN is developed. The model shows good agreement with experimental results for typical GaN dislocation densities, 5×10 8–1×10 10 cm −2, and carrier concentrations 4×10 16–1×10 18 cm −3.

Relationship of background carrier concentration and defects in GaN grown by metalorganic vapor phase epitaxy

Experimental results show that the background carrier concentrations in GaN films grown by metalorganic vapor phase epitaxy are related to defects. A thermal equilibrium method was used to calculate the background carrier concentration related to intrinsic defects in an ideal GaN crystal. The results show that the N vacancy concentration does not exceed 2×1017 cm−3 in GaN grown at temperatures ranging from 800 to 1500 K. It can be concluded that the N vacancy is one of the major sources of carriers when the carrier concentration n<2×1017 cm−3, but the main sources should be other defects when n>2×1017 cm−3; this conclusion may lead to ways for further improving the quality of GaN films.

Variation of photoluminescence with carrier concentration in GaN

Photoluminescence measurements are reported on undoped and on Ge doped single crystal epitaxial layers of GaN, having room temperature carrier concentrations (electrons) in the ranges 1.8 × 10 19 to 6.3 × 10 19cm −3 and 2.8 × 10 18 to 1.5 × 10 19cm −3 respectively. Both the previously reported donor-acceptor pair emission and a higher energy emission were observed in all samples. The intensity of the former greatly exceeded that of the latter in the undoped crystals of lower carrier concentration as it did in the Ge-doped crystals. The high energy luminescence peak was found to shift from 3.45 eV to 3.53 eV (77°K) according to increasing carrier concentration. This was found to be consistent with a model of band to band recombination across a band gap of 3.50 eV (1.6°K) for crystals with carrier concentrations in the range n > ∼ 5 × 10 18 cm -3, a Burstein shift mechanism being responsible for the observed shift of the luminescence peak.