Defect-related photoluminescence and photoluminescence excitation as a method to study the excitonic bandgap of AlN epitaxial layers: Experimental and ab initio analysis

Abstract

We report defect-related photoluminescence (PL) and its vacuum ultraviolet photoluminescence excitation (PLE) spectra of aluminum nitride layers with various layer thicknesses and dislocation densities grown on two different substrates: sapphire and silicon. The defect-related transitions have been distinguished and examined in the emission and excitation spectra investigated under synchrotron radiation. The broad PL bands of two defect levels in the AlN were detected at around 3 eV and 4 eV. In the PLE spectra of these bands, a sharp excitonic peak originating most probably from the A-exciton of AlN was clearly visible. Taking into account the exciton binding energy, the measurements allow determination of the bandgaps of the investigated AlN samples and their temperature dependencies. Next, they are compared with the literature data obtained by other experimental techniques for bulk AlN crystals and layers grown on different substrates. The obtained results revealed that the AlN bandgap depends on the substrate. The theoretical analysis using density functional theory calculations showed that the effect is induced by the tetragonal strain related to the lattice mismatch between the substrate and the AlN layer, which has a strong influence on the spectral positions of the intrinsic excitons, and consequently on the bandgap of AlN layers.

Ultrawide Bandgap Semiconductors

“…5 Kaminska et al conducted studies wherein PL and photoluminescence excitation (PLE) spectra determined that the bandgap of AlN depends on the growth substrate (Si or sapphire) due to lattice mismatch and the associated strain. 6 Theoretical work is reported by Pant et al that calculates the alloy-disorder-limited electron mobility for AlGaN, with a minimum value of 136 cm 2 /V s including all scattering mechanisms, in good agreement with experiment. 7 Electrical and thermal transport in AlGaN and AlGaN heterostructures and superlattices are likewise studied by Muhin et al 8 and Tran et al, 9 respectively.…”

Luminescence and Vacuum Ultraviolet Excitation Spectroscopy of Nanophosphors under Synchrotron Irradiation

“…The last facility provides an extremely wide excitation range for luminescence measurements (4.5-1500 eV) covering UV, VUV, and soft X-ray energy dispersion [37] and it demonstrates high potential in the luminescence studies for a wide class of inorganic materials. [10,[38][39][40][41][42][43] It is worth noting that since autumn 2021 new SUPERLUMI setup will be available for regular users at PETRA III storage ring of DESY synchrotron in Hamburg (Germany). [44]…”

Ground-State Structure of Quaternary Alloys (SiC)1−x (AlN)x and (SiC)1−x (GaN)x

“…Materials known as III-V binary nitrides (III-N = AlN, SiC, and GaN) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ] and their related alloys have recently drawn attention owing to their outstanding optoelectronic properties making them useful for many practical applications, such light-emitting diode lasers (LEDs). The reasons for their successful application are their plethora of physical characteristics, such as their small lattice parameter, large direct bandgap, high hardness, high temperature stability, good piezoelectric properties, and polytypism.…”