Photo- and Electroreflectance Spectroscopy of Low-Dimensional III-Nitride Structures
A. Drabińska
Institute of Experimental Physics, Warsaw University, Hoża 69, 00-681 Warsaw, Poland
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The review of electromodulation techniques such as photo- and electroreflectance spectroscopy is presented and illustrated using spectra of AlGaN/GaN heterostructures. By using these techniques it is possible to analyze the Franz-Keldysh oscillations to obtain the value of electric field near the surface or at interface. When additionally a constant voltage is applied to the structure, it is possible to obtain the charge distribution or the gradient of polarization present in the sample, which is of the origin of 2D electron gas at the AlGaN/GaN interface. The polarization is discussed assuming two contributions: spontaneous and piezoelectric polarization. Piezoelectric part of polarization can be obtained from X-ray diffraction, providing information about strain in the structure. Influence of light and voltage on 2D electron gas properties and depletion layer width is demonstrated using photocapacitance--voltage measurements. All results are discussed and compared with self-consistent calculations of potentials and electric fields in the structure.
DOI: 10.12693/APhysPolA.104.149
PACS numbers: 77.22.Ej, 77.65.Ly, 78.40.Fy