Scanning capacitance microscopy imaging of threading dislocations in GaN films grown on (0001) sapphire by metalorganic chemical vapor deposition

Hansen, P.; Strausser, Y. E.; Erickson, A.; Tarsa, E. J.; Kozodoy, P.; Brazel, E. G.; Ibbetson, J. P.; Mishra, Umesh K.; Narayanamurti, V.; DenBaars, Steven P.; Speck, James S.

doi:10.1063/1.121268

Cited by 266 publications

(171 citation statements)

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“…This leads us to suggest that dislocations are instead acting to impede current flow in localized regions, in effect causing a lateral inhomogeneity in which TD-localized regions restrict and divert current flow. This idea is supported by scanning capacitance microscopy studies 24 that showed evidence for significant negative charge buildup in the local vicinity of dislocations intersecting n-GaN surfaces causing higher localized Schottky barrier heights with respect to the surrounding material. This effect has also been observed by scanning Kelvin probe microscopy studies that reported an increase in surface potential of as much as 0.3-0.5 V across threading dislocations intersecting n-GaN surfaces, with a spatial full width at half maximum ͑FWHM͒ of 30-50 nm.…”

Section: B Reconciliation Of the Richardson Constant And Impact Of Tsupporting

confidence: 65%

“…Moreover, earlier studies using scanning capacitance measurements performed on MOCVD grown n-GaN samples reported local raised barrier height regions of similar length scale to the radius determined in this study. 24 Finally, it is important to note, as shown in Fig. 5͑b͒, that this correction has no effect on the extracted SBHs and so remains consistent with the SBHs extracted from the I-V-T and IPE measurements.…”

Section: ͑8͒mentioning

confidence: 99%

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Effect of threading dislocation density on Ni∕n-GaN Schottky diode I-V characteristics

Arehart

Moran

Speck

et al. 2006

Journal of Applied Physics

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110

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The impact of threading dislocation density on Ni/ n-GaN Schottky barrier diode characteristics is investigated using forward biased current-voltage-temperature ͑I-V-T͒ and internal photoemission ͑IPE͒ measurements. Nominally, identical metal-organic chemical vapor deposition grown GaN layers were grown on two types of GaN templates on sapphire substrates to controllably vary threading dislocation density ͑TDD͒ from 3 ϫ 10 7 to 7 ϫ 10 8 cm −2 . I-V-T measurements revealed thermionic emission to be the dominant transport mechanism with ideality factors near 1.01 at room temperature for both sample types. The Schottky barrier heights showed a similar invariance with TDD, with measured values of 1.12-1.13 eV obtained from fitting the I-V-T results to a thermionic emission-diffusion model. The I-V-T results were verified by IPE measurements made on the same diodes, confirming that the Ni/ n-GaN barrier heights do not show a measurable TDD dependence for the TDD range measured here. In apparent contrast to this result is that the measured forward bias I-V characteristics indicate a shift in the observed forward bias turn-on voltage such that at the higher TDD value investigated here, a larger turn-on voltage ͑lower current͒ is observed. This difference is attributed to localized current blocking by high potential barrier regions surrounding threading dislocations that intersect the Ni/ GaN interface. A simple model is presented that reconciles both the observed voltage shift and variations in the extracted Richardson constant as a function of threading dislocation density. With this model, an average local barrier surrounding dislocation of ϳ0.2 V is obtained, which diverts current flow across the forward biased Schottky interface to nondislocated regions.

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Section: B Reconciliation Of the Richardson Constant And Impact Of Tsupporting

confidence: 65%

Section: ͑8͒mentioning

confidence: 99%

Effect of threading dislocation density on Ni∕n-GaN Schottky diode I-V characteristics

Arehart

Moran

Speck

et al. 2006

Journal of Applied Physics

Self Cite

110

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“…Grains of similar size have also been observed by scanning capacitance microscopy. 13 The corresponding thresholded images are shown to accentuate the distribution of surface defects. The average measured hole diffusion lengths for both samples were the same to within experimental error; L p ϭ0.28Ϯ0.02 m. Figure 3 shows results for p-type MOCVD and n-type MBE grown GaN which also exhibited surface terminated defects.…”

Section: ͓S0003-6951͑98͒04649-x͔mentioning

confidence: 99%

Correlation between the surface defect distribution and minority carrier transport properties in GaN

Bridger

Bandić

Piquette

et al. 1998

Applied Physics Letters

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We have studied linear dislocations and surface defects in p-and n-type metalorganic chemical vapor deposition, hydride vapor phase epitaxy, and molecular beam epitaxy grown GaN films on sapphire with atomic force microscopy. The surface pits due to threading dislocations were found not to be distributed randomly but on the boundaries of growth columns. The dislocations are thought to be electrically active since the average distance between them ͑average column size͒ is comparable to minority carrier diffusion lengths as measured by electron beam induced current experiments on Schottky diodes fabricated with the same material. Diffusion lengths found for holes and electrons are on the order of L p ϭ0.28 m and L e ϭ0.16 m which corresponded to the sizes of regions free from surface dislocations in both cases and can be described by a simple model of recombination on grain boundaries. © 1998 American Institute of Physics. ͓S0003-6951͑98͒04649-X͔Gallium nitride based devices are currently of great interest for optoelectronic 1-3 as well as high power and high temperature electronics. 4,5 Since many of the performance characteristics of bipolar devices are determined by the minority carrier transport properties ͑diffusion lengths and lifetimes͒, 6 it is useful to determine how they are affected by the defect structure. It has been assumed that linear dislocations were electrically inert 7-9 since they had little effect on the performance or reliability of GaN light emitting diodes. However, the correlation between cathodoluminescence ͑CL͒ and surface morphology ͑dislocations terminating as pits in the surface͒ shown by Rosner et al. indicates that linear dislocations are important in recombination processes. 10 In this experiment, we have determined both electron and hole diffusion lengths from electron beam induced current ͑EBIC͒ measurements on material that was characterized by atomic force microscopy ͑AFM͒. We then compare the distribution of defect induced depressions on the surface with the measured diffusion lengths. Because the density of linear dislocations threading the GaN is believed to be approximately the same as those reaching the top surface of the film for thin films, 7 the two-dimensional ͑2D͒ AFM data should represent the 3D distribution of those dislocations. For thicker films, however, the density of threading dislocations reaching the surface of the film decreases with film thickness. Moreover, the AFM does not reveal all types of defects. Nevertheless, it is the nonuniform distribution of the defects and not their number that is considered here.The AFM data were obtained using a Digital Instruments Nanoscope IIIa operating in tapping mode. A cross check of the data was performed using contact AFM with oxide sharpened tips and no significant differences were found. The EBIC experiments were conducted in a JEOL6400 V electron microscope with a GW Electronics preamplifier followed by GW Electronics specimen current amplifier or Keithley 486 picoammeter. The entire apparatus was enclosed in an el...

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“…which utilizes a tip-generated ac field to cause free carriers to be attracted and repelled by the tip for two-dimensional imaging ofcarrier dynamics in GaN films. Topography and SCM images are shown in Figure 5 [12) point out, however, it is~ible that the strain fields surrounding the defects and/or the piezoelectric fields associated with these strain fields could also lead to a voltage shift in the C -V curves.…”

Section: Investigation Of Defects By Spmmentioning

confidence: 99%

“…SPM-based techniques have been employed to perform high-resolution characterization of the local electronic properties of the III-nitrides . Local electronic properties of III-nitrides were first studied by Hansen et al [12] in 1998. They employed scanning capacitance microscopy (SCM) to investigate threading dislocations in GaN.…”

Section: Introductionmentioning

confidence: 99%

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

Rodriguez

Gruverman

Nemanich

Scanning Probe Microscopy

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Recent interest in the technological potential of nitride-based semiconductors has led to the development and commercialization of a wide range of electronic devices. The nanoscale investigation of the electric properties of III-nitride thin films, bulk crystals, and heterostructures is of considerable interest for determining how interfaces, defects, and inversion domain boundaries affect device performance. The pyroelectric nature of wurtzitic III-nitrides is characterized by a spontaneous polarization that exists without the presence of an external field and by a polarization-bound surface charge. Scanning probe-based measurements of surface contact potentials and surface band bending in these materials, which are of crucial importance to device design, are summarized in this review chapter. In addition, the role of charged defects on device performance is explored by scanning probe techniques. Lastly, the measurement of polarity and of the screening mechanism of III-nitrides, which are fundamental issues for the fabrication of devices based on polarity effects, are discussed. This chapter provides a critical analysis of the contributions made by scanning probe-based techniques toward a deeper understanding of the III-nitride material system.

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Scanning capacitance microscopy imaging of threading dislocations in GaN films grown on (0001) sapphire by metalorganic chemical vapor deposition

Cited by 266 publications

References 22 publications

Effect of threading dislocation density on Ni∕n-GaN Schottky diode I-V characteristics

Effect of threading dislocation density on Ni∕n-GaN Schottky diode I-V characteristics

Correlation between the surface defect distribution and minority carrier transport properties in GaN

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

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