Abstract
We present a systematic study of surface band bending in Ga-polar n-GaN with different Si doping concentrations by angular dependent X-ray photoelectron spectroscopy (ADXPS). The binding energies of Ga 3d and N 1 s core levels in n-GaN films increase with increasing the emission angle, i. e., the probing depth, suggesting an upward surface band bending. By fitting the Ga 3d core level spectra at different emission angles and considering the integrated effect of electrostatic potential, the core level energy at the topmost surface layer is well corrected, therefore, the surface band bending is precisely evaluated. For moderately doped GaN, the electrostatic potential can be reflected by the simply linear potential approximation. However, for highly doped GaN samples, in which the photoelectron depth is comparable to the width of the space charge region, quadratic depletion approximation was used for the electrostatic potential to better understand the surface band bending effect. Our work improves the knowledge of surface band bending determination by ADXPS and also paves the way for studying the band bending effect in the interface of GaN based heterostructures.
Highlights
Group III-nitrides and related alloys have received considerable research interests in recent years mainly due to their advantages in high power/high speed device applications[1,2,3,4]
The surface band bending (BB) in Gallium Nitride (GaN) can be determined from core level binding energy, such as, Ga 3d or N 1 s, and other inherent properties of GaN, as described in the following[6,9]: Band bending(BB) = (ECL − EV)bulk + Eg − EC − (ECL − EV)surface where, (ECL − EV)bulk is the binding energy difference between core level and valance band maxima in GaN bulk which is a material constant, Eg is the band gap of GaN (3.45 eV16), EC is the position of conduction band with respect to the Fermi level, and depends on doping concentration, (ECL − EV)surface is the core level energy referenced to the Fermi level energy on GaN surface, which would change with the doping density and the surface states
We performed a systematic study on the surface band bending of Ga-polar n-GaN with different Si doping density via Angular dependent X-ray photoelectron spectroscopy (ADXPS)
Summary
Group III-nitrides and related alloys have received considerable research interests in recent years mainly due to their advantages in high power/high speed device applications[1,2,3,4]. In the band bending assessment, the magnitude of surface band bending is determined by the difference in core level energies at the topmost atomic layer and the corresponding value in the bulk, while, the measured photoelectron peak without deconvolution function at the topmost surface layer is expected to be shifted due to the integral effect, which may lead an underestimate or overestimate of the band bending extent[13,14,15]. The actual core level binding energy dependence on the detection depth can be obtained, improving the accuracy of the band bending assessment. Ga 3d core level spectra were evaluated correctly by considering the band bending due to the electrostatic potential affected by the doping density combined with localized charges on the surface. The surface band bending in different doping density GaN films are precisely determined
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