Local conductivity and surface photovoltage variations due to magnesium segregation in p-type GaN

Abstract

Conductive atomic force microscopy ͑C-AFM͒ and surface photovoltage ͑SPV͒ microscopy were used to investigate local electronic structure in p-type GaN. C-AFM imaging revealed locally reduced forward-and reverse-bias conductivity near threading dislocations. In addition, regions near threading dislocations demonstrated significantly enhanced surface photovoltage response when compared to regions away from dislocations. Analytical treatment of the surface photovoltage as a function of pertinent material properties indicated that reduced background dopant concentration is the most likely cause for the increased SPV. Both reduced conductivity and enhanced surface photovoltage are shown to be consistent with Mg segregation to dislocation cores that results in regions of locally decreased electrically active Mg concentration surrounding the dislocations.

Electrical investigation of V-defects in GaN using Kelvin probe and conductive atomic force microscopy

“…This result is in contrast to the experiments performed on sample A with the n-doped top layer but it is in agreement with similar experiments performed by Simpkins et al on p-GaN. 11 In fact, the current maxima, indicated by the dark areas, occur outside the regions of the V-defects. Increasing the applied voltage further, the current flow across the structure becomes stronger in particular areas outside the V-defects ͑not shown͒.…”

“…7,10 In contrast, other authors found a decrease in current within the V-defects for p-doped samples. 11 A rich diversity of explanations, including the formation of oxide layers with spatially varying thickness, 10 an indiffusion of the contact material along the dislocations 12 or a decrease in the electrically active doping materials within the V-defect due to segregation 11 have been suggested in order to explain the experimental results. Still, a consistent picture explaining both the local potential and the local current measurements of a V-defect in n-and in p-doped GaN heterostructures is missing.…”

The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN

“…This has the important consequence of obtaining high-Al-content Al 0.77 Ga 0.23 N doped layers of pit-free surface morphology and retained transport properties. Admittedly, 21 the formation of pits-caused by the raised Si doping level especially under the conditions of enhanced growth rate-entails high resistivity. The layer T4 in Fig.…”

Nanoscale Characterization of Electronic and Electrical Properties of III-Nitrides by Scanning Probe Microscopy

“…KPFM has been used to measure surface (contact) potentials [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] as a function of polarity, doping and surface treatment, surface band bending [22], and bare surface barrier heights [24] of III-nitrides. The measurement of these electronic properties is critical for designing devices based on III-nitrides.…”

“…They employed scanning capacitance microscopy (SCM) to investigate threading dislocations in GaN. Since then, SCM [13][14][15], electrostatic force microscopy (EFM) [16][17][18][19][20], Kelvin probe force microscopy (KPFM) [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36],conductive-tip atomic force microscopy (C-AFM) [35][36][37][38][39][40][41][42][43][44][45][46], piezoresponse force microscopy (PFM) [47][48][49][50] and scanning gate microscopy (SGM) [51] have all been employed to characterize III-nitride films and surfaces.…”