C. Mauder

Striated surface morphology and crystal orientation of m-plane GaN films grown on γ-LiAlO2(100)

Polarized in-plane and cross-sectional Raman spectra have been used to determine the crystal orientation of m-plane GaN grown on γ-LiAlO2(100) (LAO) using a three-step metalorganic vapor phase epitaxy process. The epitaxial relationship is found to be GaN(11¯00)∥LAO(100) and GaN[112¯0]∥LAO[001]. However, the stripes on the GaN surface are oriented parallel to [0001], i.e., perpendicular to the one found on striated m-plane GaN surfaces in previous studies. This unusual orientation is attributed to the changes in the Ga adatom kinetics due to the presence of a 2-nm-thick interlayer observed at the GaN/LAO interface in transmission electron microscopy.

Strong charge carrier localization interacting with extensive nonradiative recombination in heteroepitaxially grown m-plane GaInN quantum wells

The development of GaInN quantum well structures with nonpolar crystal orientation for light-emitting diodes and semiconductor lasers is currently one of the main foci of III-nitride-based optoelectronics research. One of the advantages of nonpolar orientations is the absence of polarization fields perpendicular to the quantum well plane. As a consequence, radiative recombination rates are higher compared to quantum wells on polar surfaces. However, due to high densities of threading dislocations and basal plane stacking faults in the case of heteroepitaxially grown nonpolar layers, and due to band gap inhomogeneities in the GaInN quantum wells, characterization of radiative and nonradiative recombination mechanisms is a complex challenge. So far, most published data about band gap fluctuations, charge carrier localization and internal quantum efficiency in nonpolar quantum wells are ambiguous. Here, we present temperature and excitation power density-dependent photoluminescence data featuring multiple characteristics related to strong charge carrier localization in m-plane (1–100) GaInN quantum wells. Thermally activated redistribution of charge carriers between localization sites in these quantum wells is weaker than in polar c-plane ones. The localization strength increases with higher indium concentration in the quantum wells. In the heteroepitaxially grown quantum well structures, the internal quantum efficiency is reduced even at low temperatures (T = 10 K) and especially for m-plane quantum wells with high indium mole fractions.

Effect of stress voltage on the dynamic buffer response of GaN-on-silicon transistors

Back-gated measurements on conductive silicon substrates have been performed to investigate the effect of stress voltage on the dynamic behaviour of GaN-on-silicon (GaN-on-Si) transistors. Two comparable samples were studied with the only difference being the vertical dislocation density. Results show a clear correlation between dislocation density and the ability of the GaN buffer to dynamically discharge under high stress conditions.

Formation of a Monocrystalline, M-Plane AlN Layer by the Nitridation of γ-LiAlO2(100)

Using X-ray reflectivity (XRR) measurements and high-resolution transmission electron microscopy (HRTEM), we demonstrate that a thin AlN layer is formed on top of a γ-LiAlO2(100) substrate by a nitridation process using NH3 in a metal organic vapor phase epitaxy (MOVPE) reactor. This thin layer is identified to be monocrystalline, M-plane AlN, enabling the growth of nonpolar M-plane GaN on γ-LiAlO2(100) by MOVPE. HRTEM reveals that this thin nitridation layer is grown pseudomorphically without any detectable misfit dislocations.

Effect of Different Carbon Doping Techniques on the Dynamic Properties of GaN-on-Si Buffers

The effect of different carbon doping techniques on the dynamic behavior of GaN-on-Si buffer was investigated. Intentional doping using a hydrocarbon precursor was compared with the more common autodoping technique. Breakdown and dynamic behavior of processed devices indicate that extrinsic carbon doping delivers better dynamic properties for the same blocking voltage capabilities. Modeling and simulations have revealed that charge transport across the GaN buffer is the main limiting factor during the buffer discharge process.

Irregular spectral position of E || c component of polarized photoluminescence from m-plane InGaN/GaN multiple quantum wells grown on LiAlO2

Polarized temperature dependent photoluminescence (PL) and room temperature (RT) photocurrent spectra of m-plane InGaN/GaN multiple quantum wells grown on LiAlO2 with In content xIn = 5%-30% were studied. As expected, higher xIn leads to larger strain in the wells and enhances both the splitting between the two highest valence subbands and the RT PL degree of polarization. At low temperatures, an irregular red-shift of the PL component with polarization E || c relative to E ⊥ c is observed, which is ascribed to the contribution of recombination of holes localized at band tails within the second highest valence subband.

Investigation of GaN- and CuInGaSe2-Based Heterostructures for Optoelectronic Applications

GaN-based heterostructures are widely used nowadays in many applications such as high brightness light emitting diodes (LEDs), semiconductor lasers, photodetectors, transistors, solar cells, etc. An advantage of AlxInyGa1-x-yN compound over other wide-gap materials is potential ability to cover spectral region from deep ultraviolet (UV) (∼198 nm corresponding to AlN) to infrared (∼1,770 nm corresponding to InN). Creating of effective optoelectronic devices operating in deep UV region and finding of low-cost and practically feasible substrates for GaN heteroepitaxy are the main objectives in GaN-based technology today. In the present work, several examples of fabrication of GaN-based electronic devices are considered, i. e. blue InGaN/GaN LED (∼475 nm) grown on silicon substrate; blue InGaN/GaN LED emitting polarized light (∼450 nm, polarization degree ∼0.42) grown on LiAlO2 substrate; high sensitive metal-semiconductor-metal AlGaN/GaN UV photodetector (η ∼ 4×107 A/W); AlGaN-based UV LED (300–340 nm); optically pumped AlGaN-based UV lasers emitting at 303 and 295 nm with laser threshold of ∼1 MW/cm2.

MOVPE of m-plane InGaN/GaN Buffer and LED Structures on γ-LiAlO 2

We report on deposition and properties of m-plane GaN/InGaN/AlInN structures on LiAlO 2 substrates grown by metal organic vapor phase epitaxy (MOVPE). At first, two different buffer structures, one of them including an m-plane AlInN interlayer, were investigated concerning their suitability for the subsequent coalesced single-phase m-plane GaN growth. A series of quantum well structures with different well thickness based on one of these buffers showed absence of polarization-induced electric fields verified by room temperature photoluminescence (RT PL) measurements at different excitation intensities. Furthermore, polarization-resolved PL measurements revealed a high degree of polarization (DoP) of the emitted light with an intensity ratio of 8:1 between light polarized perpendicular and parallel to the c-axis.