Determination of exciton transition energy and bowing parameter of AlGaN alloys in AlGaN/GaN heterostructure by means of reflectance measurement

Abstract

The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (E FX) of AlGaN alloys in Al x Ga 1Ϫx N/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in Al x Ga 1Ϫx N/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the E FX s obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the E FX , the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (xр0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0рxϽ0.3, the resulting bowing parameter shows a downward value of 0.53 eV.

Synchrotron-based photoluminescence excitation spectroscopy applied to investigate the valence band splittings in AlN and Al0.94Ga0.06N

“…Bowing parameters for this transition are consistently reported as 0.5 eV < b < 1 eV. [5][6][7][8][9] In contrast, the transition between CB and VB with C v 7þ character has vanishing oscillator strength for the electric field vector perpendicular to the c-direction ðE?cÞ of III-nitrides when D cf < À50 meV. This means that the emission from the CB to the highest VB is hard to detect for high aluminum content AlGaN for light normal to the csurface.…”

Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

“…[43][44][45][46] In the present work, b is taken to be 1 eV, E g (GaN) and E g (AlN) are 3.4 and 6.2 eV, respectively. Figure 3(b) shows the PL peak wavelength vs. Al content x, which is consistent with previous reports.…”

Growth and characterization of a-plane AlxGa1−xN alloys by metalorganic chemical vapor deposition

“…7(b). This value locates within the reported range from 0.17 to 1.07 eV [24][25][26]. Moreover, the PL intensity and FWHM values as a function of Al composition are summarized in Fig.…”