P. H. Chang

Magnesium Doping of In-rich InGaN

InN and In-rich InGaN were grown by metal organic vapor phase epitaxy with magnesium doping. A set of samples were grown at 550 °C, whereas a second set of samples were grown at increasing temperature with Ga content. Upon annealing, p-InGaN was obtained from the second set up to an In content above 50%, with an acceptor concentration of ~1×1019 cm-3 and a mobility of 1–2 cm2 V-1 s-1. None of the samples grown at a constant temperature of 550 °C showed a p-behavior after heat treatment. The electrical, optical, structural and morphological characteristics of the films grown were analyzed, and the leveling off of hole concentration beyond an In content of 30% was consistent with the reported decreasing activation energy of Mg with increasing In content.

Electron transport in In-rich InxGa1−xN films

We have performed electrical transport measurements on metal-organic vapor phase epitaxy grown In-rich InxGa1−xN (x=1, 0.98, and 0.92) films. Within the experimental error, the electron density in InGaN films is temperature independent over a wide temperature range (4K⩽T⩽285K). Therefore, InxGa1−xN (0.92⩽x⩽1) films can be regarded as degenerate semiconductor systems. The experimental results demonstrate that electron transport in In-rich InxGa1−xN (x=1, 0.98, and 0.92) films is metalliclike. This is supported by the temperature dependence of the density, resistivity, and mobility which is similar to that of a metal. We suggest that over the whole measuring temperature range residue imperfection scattering limits the electron mobility in In-rich InxGa1−xN (x=1, 0.98, and 0.92) films.

Schottky behavior at InN–GaN interface

In this work, GaN Schottky diodes were fabricated by depositing InN on GaN surfaces. The junction between these two materials exhibits strong rectifying behavior. The barrier heights were determined to be 1.25 eV, 1.06 eV, and 1.41 eV by current-voltage, current-voltage-temperature, and capacitance-voltage methods, respectively. These values exceed those of any other metal∕GaN Schottky barriers. Therefore, the conduction-band offset between InN and GaN should not be smaller than the barrier heights obtained here.

Application of modified transmission line model to measure p-type GaN contact

This work presented a procedure for extending the modified transmission line model to measure non-ohmic contact. This method was applied to the p-type GaN contact with the resulting sheet resistance similar to that determined by the Hall measurement. The voltage–current density (V–J) curve obtained using this procedure was also similar to that by directly analyzing the current–voltage curve of a light-emitting diode. Both results revealed the validity of this procedure. Rather than yielding a specific contact resistance for an ohmic contact, this procedure yielded a V–J curve to describe the non-ohmic contact characteristics. Similarly, this procedure could also extend the linear transmission line model to the analysis of non-ohmic contacts.

Nitride light-emitting diodes grown on Si (111) using a TiN template

Nitride light-emitting diodes (LEDs) are grown on a Si (111) substrate with a TiN template. Transmission electron microscopy and x-ray diffraction indicate that the epitaxial relation follows Si(1,1,1)‖TiN(1,1,1)‖AlN(0,0,1), Si[1,1,0]‖TiN[1,1,0], and Si[0,0,1]‖TiN[0,0,1]. The reflectance measurement and simulation results indicate that the TiN can be adopted as a reflector to mitigate the substrate absorption problem, thus increasing the extraction efficiency of nitride LEDs grown on Si.

Modified transmission line model and its application to aluminum ohmic contacts with n-type GaN

A modified transmission line model (MTLM) of ohmic contact measurement is presented. This model preserves the simplicity of the circular transmission line model but eliminates the shortcoming of the possibility of obtaining misleading results. This model was applied to n-type GaN ohmic contacts and results similar to those obtained by Hall measurement were obtained. The ohmic contact pattern used in MTLM method occasionally exists during the fabrication of several devices. In such cases, the method can be used to determine the device processing quality without the need for any other test pattern.

Effect of Buffer Layers on Electrical, Optical and Structural Properties of AlGaN/GaN Heterostructures Grown on Si

AlGaN/GaN heterostructures with different buffer layers were grown on Si substrates by metal-organic vapor phase epitaxy (MOVPE). The electrical property of the two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface was correlated with both the optical and structural quality of the GaN layer involved. A combination of two sets of high-temperature and low-temperature AlN and an ultrashort exposure to SiH4 showed the best-grown GaN, followed by a similar buffer layer without the SiH4 exposure, and a graded AlGaN buffer layer only. The enhancements in both electron mobility and 2DEG density were also accompanied by a reduced donor–acceptor pair (DAP) emission and a reduced dislocation density in the top GaN grown.

Effect of Surface Electronic States of p-Type GaN on the Blue-Light-Emitting Diodes

The surface electronic states of p-type GaN and its effect on the light-emitting diodes (LEDs) containing such p-GaN layers are studied. The surface band bending of p-GaN layers prepared from different growth conditions are determined by ultraviolet photoemission spectroscopy and X-ray photoemission spectroscopy. By either way, it is found that the surface band bending depends on the growth conditions and is reduced by increasing Mg concentration, growth temperature, and N 2 -rich ambient. A further reduction in band bending is found with a postannealing at 750°C in N 2 , resulting in a similar reduction of the operation forward voltage of the LED containing such a p-GaN layer. The mechanism involved is discussed.

Al0.15Ga0.85N∕GaN high electron mobility transistor structures grown on p-type Si substrates

We report on magnetotransport studies of Al0.15Ga0.85N/GaN high electron mobility transistor (HEMT) structures grown on p-type Si(111) substrates. Both weak localization (WL) and electron-electron interaction (EEI) correction terms to the conductivity of the SiN treated HEMT are smaller than those of the untreated HEMT. Since both WL and EEL corrections tend to decrease the conductivity of an AlGaN/GaN HEMT structure, our SiN treatment is useful for enhancing the performance of GaN-based HEMT structures grown on Si, which is compatible with the mature Silicon CMOS technology.

Transport measurements on MOVPE-grown InN films

We have performed electrical transport measurements on InN films. Our results show that the electron transport in our InN films is metallic-like, that is, within the experimental error the carrier density is temperature-independent over a wide temperature range (4 K≤T≤290 K). At low temperatures, the resistivities of our InN devices appear to saturate and show gradual increase with increasing temperatures. We suggest that residue impurity scattering limits the electron mobility in InN films. We compare our results with existing theoretical models.