GaN-AlGaN Heterostructure Field-Effect Transistors over Bulk GaN Substrates

We report on AlGaN/GaN heterostructures and heterostructurefield-effect transistors(HFETs) fabricated on high-pressure-grown bulk GaN substrates. The 2delectron gas channel exhibits excellent electronic properties with room-temperature electron Hall mobility as high as μ=1650 cm2/V s combined with a very large electron sheet density ns≈1.4×1013 cm−2.The HFET devices demonstrated better linearity of transconductance and low gate leakage, especially at elevated temperatures. We also present the comparative study of high-current AlGaN/GaN HFETs(nsμ\u3e2×1016 V−1 s−1) grown on bulk GaN, sapphire, and SiC substrates under the same conditions. We demonstrate that in the high-power regime, the self-heating effects, and not a dislocation density, is the dominant factor determining the device behavior

Radiation from shallow oxygen impurity in AlGaN/GaN HEMT structures in magnetic field

The electrically excited impurity emission from AlGaN/GaN high electron mobility transistor (HEMT) structures in external magnetic field varying from 1.2 T to 1.5 T was investigated in this work at temperature of 4.2 K. We have observed the sharp emission line at (263 ± 1) cm−1 with FWHM of (5.8 ± 0.8) cm−1, which we have attributed to radiative electronic transitions in residual oxygen impurity atoms. The blueshift of resonant transition frequency due to presence of external magnetic field was observed. The width of the peak was found to be defined mainly by the thermal broadening at 4.2 K

Graphene Schottky barrier diode acting as a semi-transparent contact to n-GaN

In this letter, we demonstrate the successful development of graphene Schottky barrier diodes (Gr SBDs), which act as an efficient semi-transparent contact to n-GaN. We show that Gr SBDs can be used for deep trap investigations in n-GaN by capacitance-based spectroscopic techniques. To demonstrate its functionality, Gr Schottky barrier diodes on an n-GaN sample grown by the metal organic vapor phase technique were fabricated and then used in the measurements of steady-state photo-capacitance (SSPC) and deep level optical spectroscopy (DLOS). It is shown that the SSPC and DLOS spectra obtained for Gr SBDs are in excellent agreement with Ni-based semi-transparent contacts to n-GaN used in this study for comparison. Deep trap levels located at Ec-3.3 eV, Ec-2.6 eV, and Ec-1.84 eV for Ni SBD and Ec-3.3 eV and Ec-2.6 eV for Gr SBD were found, respectively. The presence of a trap level with Ec-1.84 eV observed only in the Ni SBD samples suggests that this trap originates from different sample treatments prior to Schottky contact deposition. Additionally, the optical capture cross-section data (σ0) derived from DLOS were fitted using the Lucovsky model under the assumption of no lattice relaxation for all deep traps observed in this study. Discrepancies in trap concentration derived from SSPC measurements among different diodes for a trap with EC-3.3 eV were attributed to reduced light transmission through the Gr contact in the UV spectral range and the presence of some macroscopic defects related to Gr transfer to the n-GaN film

Alloy splitting of the Fe_Ga acceptor level in dilute Al_xGa_1−xN

The results of conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS measurements of the FeGa(0/−) acceptor level in dilute AlxGa1−xN layers (x ≤ 0.05) grown by MOVPE technique (metal-organic vapor phase epitaxy) on native ammono-GaN substrates are analyzed and discussed. It is shown that the electron emission signal related to the FeGa acceptor level in AlxGa1−xN splits into individual components due to aluminum fluctuations in the second-nearest neighbor (2NN) shell around the FeGa impurity atoms. The calculations of the probability of finding a given number of aluminum atoms in the 2NN shell of the FeGa defect agree well with the experimental concentrations determined from Laplace DLTS peak intensities. This finding shows that in dilute AlxGa1−xN layers grown by MOVPE, aluminum and iron atoms are randomly distributed in the material. Finally, we demonstrate that the energy level of the FeGa acceptor with no Al atoms in the 2NN shell in the AlxGa1−xN samples shifts linearly with the aluminum content and the shifts are 28 and 55 meV relative to that in GaN for the samples with x = 0.025 and 0.05, respectively.</p

Relationship between sample morphology and carrier diffusion length in gan thin films

Scanning and spot-mode cathodoluminescence investigations of homo-and hetero-epitaxial GaN films indicate a surprisingly small influence of their microstructure on overall intensity of a light emission. This we explain by a correlation between structural quality of these films and diffusion length of free carriers and excitons. Diffusion length increases with improving structural quality of the samples, which, in turn, enhances the rate of nonradiative recombination on structural defects, such as dislocations

Cathodoluminescence profiling of InGaN-based quantum well structures and laser diodes - In-plane instabilities of light emission

Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission

Influence of the substrate on the photo-luminescence dynamics in GaInN epilayers

We present results of temperature-dependent, time-resolved photoluminescence (PL) measurements on a set of Ga1-xInxN (x congruent to 0.08) layers grown at the same conditions on three different substrates: bulk (high pressure grown) GaN, SiC and Al2O3. At 9 K, the maximum of the PL occurs at about 3.1 eV. The linewidths are 48, 80 and 90 meV for the layers grown on GaN, Al2O3 and SiC, respectively. The smallest width suggests the highest homogeneity of the GaInN/GaN. The PL lifetimes (about 0.8 ns) and intensities are similar in all three samples. The spectral diffusion of the PL (shift of the PL peak energy with time) is thermally activated. The highest shift (DeltaE = 90 meV) and an activation energy E-a = 80 meV are observed in the GalnN/SiC sample, the lowest (DeltaE < 3 meV) in the GaInN/GaN sample, The smallest DeltaE (interpreted as a conduction and valence band fluctuation amplitude) found in the layer grown on GaN is due to the low dislocation concentration resulting from the good lattice matching. (C) 2002 Elsevier Science B.V. All rights reserved