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

Abstract

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.

Schottky barrier formation at the Au to rare earth doped GaN thin film interface

“…The European Physical Journal Applied Physics [28] I P E GaN 1.0 [29] I P E GaN 1.11 [24] I P E GaN 0.95 ± 0.04 [26] I P E GaN 0.97 ± 0.05 [27] I P E calculated as 1.33 ± 0.1 eV via (4). The same methods and calculations described above yielded Schottky barrier heights of 1.64 ± 0.1 eV and 1.68 ± 0.1 eV for Er:GaN and Yb:GaN, respectively.…”

“…Surface alloying can occur [14] and a large range of experimentally measured Schottky barrier heights has been reported (0.76-1.40 eV) at the Au to n-type GaN interface [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], using photoemission spectroscopy (PES), current-voltage (I-V) and capacitance voltage (C-V) characteristics, and internal photoemission [30]. However, the generally accepted value is about 1.08 eV [31].…”

Current-Transport Mechanisms in the AlInN/AlN/GaN single-channel and AlInN/AlN/GaN/AlN/GaN double-channel heterostructures

“…5(a) and (b), the SBHs were found to be a strong function of temperature and show the unusual behavior of increasing linearly with an increase in temperature from 80 K to 420 K for all of three Schottky contacts. Similar temperature dependent behaviors were reported in an early study for GaN based MS contacts [11,12,[14][15][16][17][18][19]. The ideality factor n is a measure of conformity of the diode to thermionic emission and requires the n to be constant for different temperatures and close to 1 [7].…”

“…Several investigations have been reported to analyze the dominant current-transport mechanism in GaN-based Schottky diodes. Tunneling current and thermionic field emission are both considered as dominant current transport mechanisms [8][9][10][11][12][13][14][15][16][17][18][19][20]. Evstropov et al [8,10] and Balyaev et al [13] showed that the current flow in the III-V heterojunctions is generally governed by multistep tunneling with the involvement of dislocations even at room temperature.…”

“…The high densities of threading dislocations in the epitaxial layers affect the performance reliability of the device. If many defects exist near the surface region, the electrons can easily go through the barrier by defect-assisted tunneling, thereby greatly enhancing the tunneling probability [7][8][9][10][11][12][13][14][15].…”