Free and bound excitons in thin wurtzite GaN layers on sapphire

Abstract

Free and bound excitons have been studied by photoluminescence in thin (1-10 µm) wurtzite-undoped GaN, n-type GaN:Si as well as p-type GaN:Mg and GaN:Zn layers grown by metal-organic chemical vapour phase deposition (MOCVD). An accurate value for the free A exciton binding energy and an estimate for the isotropically averaged hole mass of the uppermost 9 valence band are deduced from the data on undoped samples. The acceptor-doped samples reveal recombination lines which are attributed to excitons bound to Mg 0 and Zn 0 respectively. These lines are spectrally clearly separated and the exciton localization energies are in line with Haynes' rule. Whenever a comparison is possible, it is found that the exciton lines in these thin MOCVD layers are ultraviolet-shifted by 20 to 25 meV as compared to quasi-bulk (≥ 100 µm) samples. This effect is interpreted in terms of the compressive hydrostatic stress component which thin GaN layers experience when grown on sapphire with an AlN buffer layer.

Exciton and donor - acceptor recombination in undoped GaN on Si(111)

“…From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37]. Lower values for E LD have been found in thin GaN layers grown on sapphire or SiC (down to 5.9 meV [5]), probably due to strain. For bulk or thick layers the same value E LD = 7.2 meV was reported [4], whereas values of 6.1 meV [12] and 7.4 meV [13] were found for GaN/GaN.…”

“…For kT comparable to E LD (=7.2 meV), the excitons are thermally released from the shallow donor to contribute to FX emission [5,17,36]. From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37].…”

Exciton and donor - acceptor recombination in undoped GaN on Si(111)

“…From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37]. Lower values for E LD have been found in thin GaN layers grown on sapphire or SiC (down to 5.9 meV [5]), probably due to strain. For bulk or thick layers the same value E LD = 7.2 meV was reported [4], whereas values of 6.1 meV [12] and 7.4 meV [13] were found for GaN/GaN.…”

“…For kT comparable to E LD (=7.2 meV), the excitons are thermally released from the shallow donor to contribute to FX emission [5,17,36]. From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37].…”

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces

“…The inset displays spectra of the high-energy line of the Y 4 doublet for different magnetic fields. Fits of the data with eq yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN . For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/IDB* quantum wire exciton.…”

“…Fits of the data with eq 1 yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN. 37 For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/ IDB* quantum wire exciton. This value is much larger than the calculated one (E B = 7 meV) and thus implies that the I 1 BSF/ IDB* junction actually exhibits a type-I band alignment with a strong confinement of both electrons and holes.…”

Exciton spectra and spin - orbit splitting in GaN epitaxial films

“…This is almost certainly due to the introduction of varying amounts of strain into the films during cooling from the growth temperature to room temperature, as a result of differences in thermal expansion coefficient between substrate and film. This has been noted by various authors previously (Monemar et al 1995, Mohammad et al 1995, Merz et al 1996 and appears to be well established. The observation made by Gil et al is that the energies of the A, B and C excitons show a clear correlation.…”

Exciton and donor - acceptor recombination in undoped GaN on Si(111)

“…From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37]. Lower values for E LD have been found in thin GaN layers grown on sapphire or SiC (down to 5.9 meV [5]), probably due to strain. For bulk or thick layers the same value E LD = 7.2 meV was reported [4], whereas values of 6.1 meV [12] and 7.4 meV [13] were found for GaN/GaN.…”

“…For kT comparable to E LD (=7.2 meV), the excitons are thermally released from the shallow donor to contribute to FX emission [5,17,36]. From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37].…”

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces

“…The inset displays spectra of the high-energy line of the Y 4 doublet for different magnetic fields. Fits of the data with eq yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN . For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/IDB* quantum wire exciton.…”

“…Fits of the data with eq 1 yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN. 37 For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/ IDB* quantum wire exciton. This value is much larger than the calculated one (E B = 7 meV) and thus implies that the I 1 BSF/ IDB* junction actually exhibits a type-I band alignment with a strong confinement of both electrons and holes.…”

Exciton spectra and spin - orbit splitting in GaN epitaxial films

“…This is almost certainly due to the introduction of varying amounts of strain into the films during cooling from the growth temperature to room temperature, as a result of differences in thermal expansion coefficient between substrate and film. This has been noted by various authors previously (Monemar et al 1995, Mohammad et al 1995, Merz et al 1996 and appears to be well established. The observation made by Gil et al is that the energies of the A, B and C excitons show a clear correlation.…”

Exciton and donor - acceptor recombination in undoped GaN on Si(111)

“…From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37]. Lower values for E LD have been found in thin GaN layers grown on sapphire or SiC (down to 5.9 meV [5]), probably due to strain. For bulk or thick layers the same value E LD = 7.2 meV was reported [4], whereas values of 6.1 meV [12] and 7.4 meV [13] were found for GaN/GaN.…”

“…For kT comparable to E LD (=7.2 meV), the excitons are thermally released from the shallow donor to contribute to FX emission [5,17,36]. From equation ( 5), we estimate E D = 36 ± 0.5 meV, in agreement with the precise value E D = 35.5 meV obtained by Fourier transform infrared absorption on thick films [37].…”

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces

“…The inset displays spectra of the high-energy line of the Y 4 doublet for different magnetic fields. Fits of the data with eq yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN . For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/IDB* quantum wire exciton.…”

“…Fits of the data with eq 1 yield a value of E B = 24.3 meV for the X A transition, in reasonable agreement with the exciton binding energy of 26 meV reported for bulk GaN. 37 For the line at 3.366 eV, a much smaller blueshift is observed, corresponding to a value of E B = 67.5 meV for the I 1 BSF/ IDB* quantum wire exciton. This value is much larger than the calculated one (E B = 7 meV) and thus implies that the I 1 BSF/ IDB* junction actually exhibits a type-I band alignment with a strong confinement of both electrons and holes.…”

Exciton spectra and spin - orbit splitting in GaN epitaxial films

“…This is almost certainly due to the introduction of varying amounts of strain into the films during cooling from the growth temperature to room temperature, as a result of differences in thermal expansion coefficient between substrate and film. This has been noted by various authors previously (Monemar et al 1995, Mohammad et al 1995, Merz et al 1996 and appears to be well established. The observation made by Gil et al is that the energies of the A, B and C excitons show a clear correlation.…”