Studies of the origin of the yellow luminescence band, the nature of nonradiative recombination and the origin of persistent photoconductivity in n-GaN films

Concentrations of deep hole traps were measured in a set of hydride vapor phase epitaxy grown samples with thicknesses varying from 2.6 to 68 m. Results were obtained from low temperature capacitance-voltage measurements before and after illumination and from deep level transient spectroscopy measurements with optical injection ͑ODLTS͒. The former revealed the presence of high densities ͑ϳ10 15 to 10 16 cm Ϫ3 ͒ of hole traps whose concentration decreased with sample thickness in a manner similar to that found for the dislocation density. Capacitance versus temperature measurements in the dark and after illumination suggested that these traps form a band of states rather than a single level in the GaN band gap. It is suggested that such states could be associated with dislocations. The main hole traps observed by ODLTS were deep hole traps, of energy near E v ϩ0.9 eV. Their density was also observed to substantially decrease with sample thickness.

Section: Fig 2 1/cmentioning

confidence: 99%

Deep hole traps in n-GaN films grown by hydride vapor phase epitaxy

Polyakov

Smirnov

Говорков

et al. 2002

“…Evaluating this ex-pression requires knowledge of the room temperature capture cross section of the traps being investigated in this work. While such data are not available for the traps considered here, capture cross sections in HR and n-type GaN have been reported [23][24][25] in a broad range from roughly 10 Ϫ23 cm 2 to 10 Ϫ15 cm 2 . Polyakov et al 25 have reported capture cross sections for GaN near room temperature for the E2 center ͓ c (278 K)ϭ4ϫ10 Ϫ20 cm 2 ] and the E4 center ͓ c (385 K)ϭ3.3ϫ10 Ϫ23 cm 2 ].…”

Section: ͑29͒mentioning

confidence: 99%

Photoionization spectroscopy of traps in GaN metal-semiconductor field-effect transistors

Klein¹,

Binari²,

Freitas³

et al. 2000

Measurements of the spectral and intensity dependences of the optically-induced reversal of current collapse in a GaN metal-semiconductor field-effect transistor ͑MESFET͒ have been compared to calculated results. The model assumes a net transfer of charge from the conducting channel to trapping states in the high-resistivity region of the device. The reversal, a light-induced increase in the trap-limited drain current, results from the photoionization of trapped carriers and their return to the channel under the influence of the built-in electric field associated with the trapped charge distribution. For a MESFET in which two distinct trapping centers have been spectrally resolved, the experimentally measured dependence upon light intensity was fitted using this model. The two traps were found to have very different photoionization cross-sections but comparable concentrations (4ϫ10 11 cm Ϫ2 and 6ϫ10 11 cm Ϫ2 ͒, suggesting that both traps contribute comparably to the observed current collapse. ͓S0021-8979͑00͒00417-5͔

“…[1][2][3][4] Because of the large band gap, the applications of Al x Ga 1−x N are extensive, such as for visible-blind ultraviolet detectors, laser diodes, and short-wave lightemitting diodes ͑LEDs͒. 5,6 High-quality AlGaN/GaN heterostructures have been shown to contain two-dimensional electron gas ͑2DEG͒, which has attracted special interest due to its potential applications in high mobility transistors operating at high power and high temperature levels. [7][8][9][10] The device structures are usually grown on highly lattice-mismatched substrates, such as sapphire, 11 SiC, 12 or Si.…”

Section: Introductionmentioning

confidence: 99%

The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

Arslan

Bütün

Li̇şesi̇vdi̇n

et al. 2008

In the present study, we reported the results of the investigation of electrical and optical measurements in Al x Ga 1−x N / GaN heterostructures ͑x = 0.20͒ that were grown by way of metal-organic chemical vapor deposition on sapphire and SiC substrates with the same buffer structures and similar conditions. We investigated the substrate material effects on the electrical and optical properties of Al 0.20 Ga 0.80 N / GaN heterostructures. The related electrical and optical properties of Al x Ga 1−x N / GaN heterostructures were investigated by variable-temperature Hall effect measurements, photoluminescence ͑PL͒, photocurrent, and persistent photoconductivity ͑PPC͒ that in turn illuminated the samples with a blue ͑ = 470 nm͒ light-emitting diode ͑LED͒ and thereby induced a persistent increase in the carrier density and two-dimensional electron gas ͑2DEG͒ electron mobility. In sample A ͑Al 0.20 Ga 0.80 N / GaN/ sapphire͒, the carrier density increased from 7.59ϫ 10 12 to 9.9ϫ 10 12 cm −2 via illumination at 30 K. On the other hand, in sample B ͑Al 0.20 Ga 0.80 N / GaN/ SiC͒, the increments in the carrier density were larger than those in sample A, in which it increased from 7.62ϫ 10 12 to 1.23ϫ 10 13 cm −2 at the same temperature. The 2DEG mobility increased from 1.22ϫ 10 4 to 1.37ϫ 10 4 cm −2 / V s for samples A and B, in which 2DEG mobility increments occurred from 3.83ϫ 10 3 to 5.47ϫ 10 3 cm −2 / V s at 30 K. The PL results show that the samples possessed a strong near-band-edge exciton luminescence line at around 3.44 and 3.43 eV for samples A and B, respectively. The samples showed a broad yellow band spreading from 1.80 to 2.60 eV with a peak maximum at 2.25 eV with a ratio of a near-band-edge excitation peak intensity up to a deep-level emission peak intensity ratio that were equal to 3 and 1.8 for samples A and B, respectively. Both of the samples that were illuminated with three different energy photon PPC decay behaviors can be well described by a stretched-exponential function and relaxation time constant as well as a decay exponent ␤ that changes with the substrate type. The energy barrier for the capture of electrons in the 2DEG channel via the deep-level impurities ͑DX-like centers͒ in AlGaN for the Al 0.20 Ga 0.80 N / GaN/sapphire and Al 0.20 Ga 0.80 N / GaN/ SiC heterojunction samples are 343 and 228 meV, respectively. The activation energy for the thermal capture of an electron by the defects ⌬E changed with the substrate materials. Our results show that the substrate material strongly affects the electrical and optical properties of Al 0.20 Ga 0.80 N/GaN heterostructures. These results can be explained with the differing degrees of the lattice mismatch between the grown layers and substrates.