Z. T. Chen

Improved performance of InAlN-based Schottky solar-blind photodiodes

The authors report the growth of InxAl1−xN with high crystal quality by metal organic chemical vapor deposition, the Pd/InxAl1−xN Schottky contacts with reverse current densities as low as 6.0×10−7 A/cm2 at −5 V and 2.1×10−5 A/cm2 at −10 V, and consequently significant improvement in the performance of InAlN-based Schottky solar-blind photodiodes with peak responsivity of 133 mA/W at 242 nm, corresponding to a quantum efficiency of 68.5%. The illumination is detectable under the intensity as weak as 10 nW/cm2. The rejection ratios by 300 nm are one order of magnitude for 10 nW/cm2 illumination and three orders of magnitude for 1 μW/cm2 illumination.

Compositional instability in InAlN/GaN lattice-matched epitaxy

The InxAl1−xN/GaN system is found to show compositional instability at the lattice-matched composition (x = 0.18) in epitaxial layers grown by metal organic chemical vapor deposition. The breakdown in compositional homogeneity is triggered by threading dislocations with a screw component propagating from the GaN underlayer, which tend to open up into V-grooves at a certain thickness of the InxAl1−xN layer. The V-grooves coalesce at ∼200 nm and are filled with material that exhibits a significant drop in indium content and a broad luminescence peak. Transmission electron microscopy suggests that the structural breakdown is due to heterogeneous nucleation and growth at the facets of the V-grooves.

Effect of n-GaN thickness on internal quantum efficiency in InxGa1-xN multiple-quantum-well light emitting diodes grown on Si (111) substrate

The mechanism of the effect of n-GaN thickness on the internal quantum efficiency (IQE) in InxGa1-xN multiple-quantum-wells (MQWs) grown on GaN/Si by means of metal organic chemical vapor deposition has been investigated by x-ray diffractometry, photoluminescence, and transmission electron microscopy. It is found that the increasing n-GaN thickness obviously improves the IQE in InxGa1-xN MQWs. It is clarified that the threading dislocation density (TDD) directly determines the V-defect density and the V-defect density is lower than the TDD. As the n-GaN thickness increases from 1.0 to 2.0 μm, the TDD significantly decreases by one order of magnitude. The V-defect density obviously reduces from 3.9 × 109 cm−2 to 8.7 × 108 cm−2, while the IQE in InxGa1-xN MQWs is improved from 28.3 to 44.6%. As the GaN thickness increases, the V-defect density in the InxGa1-xN MQW decreases due to the reduction of TDD in GaN, and subsequently the nonradiative recombination centers are effectively eliminated due to the reduc...

Schottky Barrier Height Inhomogeneity-Induced Deviation From Near-Ideal Pd/InAlN Schottky Contact

A Pd/InAlN Schottky diode with leakage current as low as 1.01 × 10-6 A/cm2 at -5 V at 300 K has been fabricated. It is found that the current-voltage (I-V) characteristics of Pd/InAlN Schottky contact can be quantitatively described by taking into account the inhomogeneity of Schottky barrier height (SBH), and the SBH inhomogeneity is the main cause for the significant deviation from an ideal Schottky contact. The SBH inhomogeneity is suggested to be related to the quantum dotlike structure on InAlN surface, indicating the importance of surface effect to the investigations on those devices involving InAlN-based Schottky contact.

Effect of strain on quantum efficiency of InAlN-based solar-blind photodiodes

A series of InxAl1−xN-based Schottky solar-blind photodiodes are fabricated on the InxAl1−xN epilayers with high and very close crystal qualities. The quantum efficiency varies from 14.5% to 68.5%. The microstructure and strain state of epilayers are investigated in detail. It is found that the quantum efficiency of photodiode depends on the strain state in InxAl1−xN films. This indicates that adjusting the strain state in InxAl1−xN film is one of the promising approaches to optimize the performance of InAlN-based solar-blind photodiode.

Demonstration on GaN-based light-emitting diodes grown on 3C-SiC/Si(111)

GaN-based light-emitting diodes (LEDs) grown on template of 3C-SiC/Si(111) were demonstrated. The structural properties have been investigated systematically by means of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. It is found that the intermediate layer (IL) of 3C-SiC leads to not only a significant improvement in the crystalline quality of GaN, but also better interfaces between the buffer layer and the initial layers of strained-layer superlattice. The device properties were also evaluated using the measurements of current-voltage, electroluminescence, and light output power-current. Compared to conventional LEDs that do not contain 3C-SiC IL, the device with IL exhibits enhanced output power by more than 200% at an injection current of 20 mA, and the operating voltage is slightly increased from 3.7 to 3.9 V. These results indicate that using 3C-SiC as IL is one of the promising approaches to improve the performance of LEDs on silicon.

Photoluminescence studies of high-quality InAlN layer lattice-matched to GaN grown by metal organic chemical vapor deposition

Temperature-dependent photoluminescence (PL) measurements have been performed on high-quality InAlN layers lattice-matched (LM) to GaN with different thicknesses. It is found that the PL is consisted of two components denoted as IH (high-energy side) and IL (low-energy side), respectively. IH is attributed to exciton luminescence of bulk InAlN with linewidth comparable to those calculated under the assumption of perfect random alloy. While IL is attributed to the emission from the quantum-dotlike structure on the surface of InAlN, revealing the importance of surface effect to the investigations related to InAlN LM to GaN.

Threading dislocation-governed degradation in crystal quality of heteroepitaxial materials: The case of InAlN nearly lattice-matched to GaN

The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN.

High Performance of GaN-Based Light Emitting Diodes Grown on 4-in. Si(111) Substrate

We have demonstrated GaN-based light emitting diodes (LEDs) grown by metal-organic chemical vapor deposition on 4-in. Si(111) substrates. The structural property has been revealed by the measurement of X-ray diffraction. One of the full widths at half maximum of ω-scans of the GaN (0002) reflection is around 630 arcsec. Also, it can be found that the GaN epitaxial quality can be improved by increasing the thickness of n-GaN. The device properties have been evaluated through current–voltage, electroluminescence, and light output power–current measurements. As the n-GaN thickness increases from 1 to 2 µm, the light output powers of the LEDs have enhanced approximately two times under the injection current of 20 mA. Moreover, the maximum values of respective external quantum efficiency are achieved as 0.3 and 0.6%, respectively.

Deep Traps in InAlN Lattice-Matched to GaN Grown by Metal Organic Chemical Vapor Deposition Studied by Deep-Level Transient Spectroscopy

InxAl1-xN lattice-matched to GaN with recording crystal quality have been grown on AlN/sapphire template by metal organic chemical vapor deposition. The width at half maximums (FWHMs) of X-ray diffraction (XRD) ω-rocking curves are as low as 100 arcsec for (0002) reflection and 248 arcsec for (1012) reflection, respectively. Deep level transient spectroscopy (DLTS) technique has been employed to investigate the deep traps in InAlN. Three deep traps were observed with activation energies of E1 = 0.351 ±0.018, E2 = 0.404 ±0.027, and E3 = 0.487 ±0.026 eV, respectively. The capture kinetic behaviors of E1 and E3 were investigated, and it is believed that E1 is associated with point defects while E3 is related to dislocations.