Marian Caliebe

Comparative study of polar and semipolar (112⁻2) InGaN layers grown by metalorganic vapour phase epitaxy

InGaN layers were grown simultaneously on (112¯2) GaN and (0001) GaN templates by metalorganic vapour phase epitaxy. At higher growth temperature (≥750 °C), the indium content (<15%) of the (112¯2) and (0001) InGaN layers was similar. However, for temperatures less than 750 °C, the indium content of the (112¯2) InGaN layers (15%–26%) were generally lower than those with (0001) orientation (15%–32%). The compositional deviation was attributed to the different strain relaxations between the (112¯2) and (0001) InGaN layers. Room temperature photoluminescence measurements of the (112¯2) InGaN layers showed an emission wavelength that shifts gradually from 380 nm to 580 nm with decreasing growth temperature (or increasing indium composition). The peak emission wavelength of the (112¯2) InGaN layers with an indium content of more than 10% blue-shifted a constant value of ≈(50–60) nm when using higher excitation power densities. This blue-shift was attributed to band filling effects in the layers.

High Bandwidth Freestanding Semipolar (11–22) InGaN/GaN Light-Emitting Diodes

Freestanding semipolar (11-22) indium gallium nitride (InGaN) multiple-quantum-well light-emitting diodes (LEDs) emitting at 445 nm have been realized by the use of laser lift-off (LLO) of the LEDs from a 50-μm-thick GaN layer grown on a patterned (10-12) r-plane sapphire substrate (PSS). The GaN grooves originating from the growth on PSS were removed by chemical mechanical polishing. The 300 μm × 300 μm LEDs showed a turn-on voltage of 3.6 V and an output power through the smooth substrate of 0.87 mW at 20 mA. The electroluminescence spectrum of LEDs before and after LLO showed a stronger emission intensity along the [11-23]InGaN/GaN direction. The polarization anisotropy is independent of the GaN grooves, with a measured value of 0.14. The bandwidth of the LEDs is in excess of 150 MHz at 20 mA, and back-to-back transmission of 300 Mbps is demonstrated, making these devices suitable for visible light communication (VLC) applications.

Development of semipolar (11-22) LEDs on GaN templates

We report on blue and green light-emitting-diodes (LEDs) grown on (11-22)-GaN templates. The templates were created by overgrowth on structured r-plane sapphire substrates. Low defect density, 100 mm diameter GaN templates were obtained by metal organic vapour phase epitaxy (VPE) and hydride VPE techniques. Chemical-mechanical polishing was used to obtain smooth surfaces for the subsequent growth of LED structures. Ohmic contacts to the p-type GaN were obtained despite the lower activated acceptor levels. The LEDs show excellent output power and fast carrier dynamics. Freestanding LEDs have been obtained by use of laser-lift-off. The work is the result of collaboration under the European Union funded ALIGHT project.

Three-dimensional cathodoluminescence characterization of a semipolar GaInN based LED sample

A semipolar GaInN based light-emitting diode (LED) sample is investigated by three-dimensionally resolved cathodoluminescence (CL) mapping. Similar to conventional depth-resolved CL spectroscopy (DRCLS), the spatial resolution perpendicular to the sample surface is obtained by calibration of the CL data with Monte-Carlo-simulations (MCSs) of the primary electron beam scattering. In addition to conventional MCSs, we take into account semiconductor-specific processes like exciton diffusion and the influence of the band gap energy. With this method, the structure of the LED sample under investigation can be analyzed without additional sample preparation, like cleaving of cross sections. The measurement yields the thickness of the p-type GaN layer, the vertical position of the quantum wells, and a defect analysis of the underlying n-type GaN, including the determination of the free charge carrier density. The layer arrangement reconstructed from the DRCLS data is in good agreement with the nominal parameters defined by the growth conditions.A semipolar GaInN based light-emitting diode (LED) sample is investigated by three-dimensionally resolved cathodoluminescence (CL) mapping. Similar to conventional depth-resolved CL spectroscopy (DRCLS), the spatial resolution perpendicular to the sample surface is obtained by calibration of the CL data with Monte-Carlo-simulations (MCSs) of the primary electron beam scattering. In addition to conventional MCSs, we take into account semiconductor-specific processes like exciton diffusion and the influence of the band gap energy. With this method, the structure of the LED sample under investigation can be analyzed without additional sample preparation, like cleaving of cross sections. The measurement yields the thickness of the p-type GaN layer, the vertical position of the quantum wells, and a defect analysis of the underlying n-type GaN, including the determination of the free charge carrier density. The layer arrangement reconstructed from the DRCLS data is in good agreement with the nominal parameters ...

Intentional anisotropic strain relaxation in ( 112¯2) oriented Al1−xInxN one-dimensionally lattice matched to GaN

We report on ( 112¯2) oriented Al1−xInxN grown by low pressure metal organic vapor phase epitaxy on ( 112¯2) GaN templates on patterned r-plane sapphire. The indium incorporation efficiency as well as the growth rate of ( 112¯2) oriented layers are similar to c-plane oriented Al1−xInxN layers. Deposition of thick Al1−xInxN layers does not lead to additional roughening like in case of c-plane oriented Al1−xInxN. Independent of the thickness, the degree of relaxation of layers lattice matched in m-direction is in the range of 33%–45% in [ 112¯3¯]-direction. Associated with the relaxation in [ 112¯3¯]-direction, there is a tilt of the Al1−xInxN layers around the [ 11¯00] axis due to slip of threading dislocations on the basal (0001)-plane. Relaxation in m-direction is not observable for layers lattice matched in [ 112¯3¯] direction. The possibility to adjust the lattice parameter of AlInN in [ 112¯3¯] direction without changing the lattice parameter in m-direction by anisotropic strain relaxation opens up op...

Stacking fault emission in GaN: Influence of n-type doping

We present spatially and spectrally resolved cathodoluminescence investigations on the cross section of semipolar (112¯2) gallium nitride epitaxial layers with high background doping level. The locally varying high carrier concentration leads in emission to a free electron recombination band (FERB) governed on the high energy side by conduction band filling. For the basal plane stacking fault (BSF) of type I1, typically emitting at ≈3.41 eV in low doped GaN, we find a blue shift in emission correlated to the FERB high energy tail. This shift can be perfectly modeled and understood in a quantum well model for the BSF, taking also into account the varying doping level in the barrier region. Thus, the carrier concentration can be finally calculated either from the actual position of the I1 BSF or alternatively from the FERB-related near band edge emission.