Structural and optical properties of Al_x In_y Ga_1−x−y N quaternary alloys grown on sapphire substrates by molecular beam epitaxy

Abstract

Purpose

The purpose of this paper is to study the structural and optical characterization of Al_x In_y Ga_1−x−y N quaternary epilayers, which were grown on c‐plane (0001) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy technique with indium (In) mole fraction y ranging from 0.0 to 0.1 and constant aluminum (Al) mole fraction x=0.06.

Design/methodology/approach

High‐resolution X‐ray diffraction rocking curve (HRXRD‐RC), scanning electron microscopy (SEM), energy dispersive X‐ray spectrometry (EDX), and photoluminescence (PL) spectroscopy have been measured on quaternary Al_x In_y Ga_1−x−y N thin films at room temperature.

Findings

HRXRD‐RC measurements confirmed that the Al_x In_y Ga_1−x−y N alloys had wurtzite structure. SEM images, element composition analysis by EDX, provided the evidence to show the existence of defects inside the samples contaminated by silicon from previous growth leading to nonuniformity of the epilayers, which caused decreased in the quality of the samples. PL spectra show reducing of the integrated intensity and an increasing red shift with increasing in content with reference to the ternary sample Al_0.06Ga_0.94N. The existence of a large amount of nonradiative recombination centers are responsible for the reduced the luminescence and the red shift provided evidence to an increase in composition inside the Al_x In_y Ga_1−x−y N quaternary alloys. Photoluminescence is used to determine the behavior of the near band edge emission represent the energy band gap of the quaternary films. The energy band gap decreases with increasing In composition from 0.01 to 0.1 mole fraction. This trend is expected since the incorporation of in reduced the energy band gap of ternary Al_0.06Ga_0.94N (3.529 eV). We have also investigated the bowing parameter of the variation of energy band gaps and found it to be very sensitive on in composition. A value of b=10.95 have been obtain for our quaternary Al_x In_y Ga_1−x−y N alloys.

Originality/value

This study on quaternary samples described in this paper, clearly indicates that the present of defects due to impurity contaminations has a dominant role in determining the structural and optical properties of Al_x In_y Ga_1−x−y N quaternary alloys.

Citation

Abid, M.A., Abu Hassan, H., Hassan, Z., Ng, S.S., Mohd Bakhori, S.K. and Abd Raof, N.H. (2010), "Structural and optical properties of Al_x In_y Ga_1−x−y N quaternary alloys grown on sapphire substrates by molecular beam epitaxy", Microelectronics International, Vol. 27 No. 3, pp. 148-153. https://doi.org/10.1108/13565361011061957