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We report the effect of V-shaped pit size, inverted hexagonal pits embedded in InGaN multiple quantum well, on the reverse leakage current of InGaN light-emitting diodes (LEDs). It was found that the reverse leakage current of InGaN LEDs with larger V-shaped pits is significantly reduced from 1.80 mA down to 3.84 nA at -30~V by several orders of magnitude. We claim that this improvement is accounted for increased Poole-Frenkel barrier height of carrier trapped at the deep centers via enlarged V-pit formation, consequently resulting in lower reverse current of InGaN LEDs. [ABSTRACT FROM AUTHOR]

We investigate the reverse leakage characteristics of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrate by metal–organic chemical vapor deposition. The reverse leakage characteristics of InGaN/GaN LED on silicon are measured as low as \sim10 nA at -5 V and -10 \mu\A at -15 V. Temperature-dependent current–voltage ( I–V) measurements of LED devices reveal that the reverse leakage current mechanism is mainly attributed to the field-enhanced thermionic emission, also known as Poole–Frenkel emission, of carriers from deep centers within the space charge region up to \sim-18 V. The analysis of T–I –V curve yields the calculation of the coefficient of the Poole–Frenkel effect (\1.12 \times \10^-4\ \eV\cdot \V^-1/2\cdot\cm^1/2) and activation energies of carriers ( \sim214 meV at -5 V). With further increase of reverse bias, up to - 40 V, LED devices exhibit the onset of space-charge-limited leakage current mechanism without any local breakdown. [ABSTRACT FROM AUTHOR]

We report the characteristics of forward tunneling current in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) grown on Si (111) substrate. Temperature-variable current-voltage (I-V) measurement from 80 K to 400 K reveals that forward current regimes can be distinguished by corresponding slopes in semi-logarithmic plot, which are associated with different forward conduction mechanisms of InGaN LED. Temperature-insensitive tunneling behavior appears to be dominant at low current injection regime for InGaN LEDs on Si. Conductive atomic force microscopy analysis indicates that V-pits associated with threading dislocations could be main leakage path of forward tunneling current of InGaN LED on Si. [ABSTRACT FROM AUTHOR]

Abstract: GaN-based light-emitting-diodes (LEDs) on (111) Si substrates with internal quantum efficiency (IQE) exceeding 50% have been successfully grown by metal organic vapor phase epitaxy (MOVPE). 3.5μm thick crack-free GaN epitaxial layers were grown on the Si substrates by the re-growth method on patterned templates. Series of step-graded Al x Ga1−x N epitaxial layers were used as the buffer layers to compensate thermal tensile stresses produced during the post-growth cooling process as well as to reduce the density of threading dislocations (TDs) generated due to the lattice mismatches between III-nitride layers and the silicon substrates. The light-emitting region consisted of 1.8μm thick n-GaN, 3 periods of InGaN/GaN superlattice, InGaN/GaN multiple quantum wells (MQWs) designed for a peak wavelength of about 455nm, an electron blocking layer (EBL), and p-GaN. The full-widths at half-maximum (FWHM) of (0002) and (10−12) ω-rocking curves of the GaN epitaxial layers were 410 and 560arcsec, respectively. Cross-sectional transmission electron microscopy (TEM) investigation revealed that the propagation of the threading dislocations was mostly limited to the interface between the last Al x Ga1−x N buffer and n-GaN layers. The density of the threading dislocations induced pits of n-GaN, as estimated by atomic force microscopy (AFM), was about 5.5×108 cm−2. Temperature dependent photoluminescence (PL) measurements with a relative intensity integration method were carried out to estimate the internal quantum efficiency (IQE) of the light-emitting structures grown on Si, which reached up to 55%. [Copyright &y& Elsevier]