Double-layer Passivation Research Articles

Performance comparison of flip-chip blue-light microLEDs with various passivation

In this study, arrays of μLEDs in four different sizes (5 × 5 μm2, 10 × 10 μm2, 25 × 25 μm2, 50 × 50 μm2) were fabricated using a flip-chip bonding process. Two passivation processes were investigated with one involving a single layer of SiO2 deposited using plasma-enhanced chemical vapor deposition (PECVD) and the other incorporating Al2O3 deposited by atomic layer deposition (ALD) beneath the SiO2 layer. Owing to superior coverage and protection, the double-layers passivation process resulted in a three-order lower leakage current of μLEDs in the 5 μm chip-sized μLED arrays. Furthermore, higher light output power of μLEDs was observed in each chip-sized μLED array with double layers passivation. Particularly, the highest EQE value 21.9% of μLEDs array with 5 μm × 5 μm chip size was achieved with the double-layers passivation. The EQE value of μLEDs array was improved by 4.4 times by introducing the double-layers passivation as compared with that of μLEDs array with single layer passivation. Finally, more uniform light emission patterns were observed in the μLEDs with 5 μm × 5 μm chip size fabricated by double-layer passivation process using ImageJ software.

Anodized lamellar Ni-Ni3Si template for electrodeposition of micro-nanostructures

The lamellar Ni-Ni3Si template has the potential for various applications, such as magnetic arrays, layered magnetoelectric materials, electrode materials, and supercapacitors via electrodeposition. However, accurately electrodepositing other materials within the microchannels of the lamellar Ni-Ni3Si template remains a challenge. In this work, the lamellar Ni-Ni3Si template was anodized in 0.1 M oxalic acid (H2C2O4) to achieve accurate deposition of other materials within the microchannels of the lamellar Ni-Ni3Si template. After anodization, the non-anodized and anodized lamellar Ni-Ni3Si templates were subjected to various characterization techniques, including electrochemical impedance spectroscopy, Mott-Schottky analysis, X-ray diffraction and X-ray photoelectron spectroscopy. The study revealed that the optimal anodization potential is 1.2 VSCE, which generated a double-layer passivation film mainly comprised of Ni(OH)2 and SiO2, with a small amount of NiO and Ni2SiO4. Furthermore, cobalt was electrodeposited on non-anodized and anodized lamellar Ni-Ni3Si templates. The results showed that the passive film of the anodized lamellar Ni-Ni3Si template effectively inhibits cobalt nucleation on the surface and sidewalls of the β-Ni3Si sheets and facilitates cobalt deposition within the microchannels. This work provides a novel lamellar metallic template for the electrodeposition of micro-nanostructures.

Electrical properties of plasma-free ultra-low-temperature ALD ZnS passivation on p-type HgCdTe

ZnS thin films have been successfully deposited using metal organic compound with ultra-low-temperature atomic layer deposition (ULT-ALD) at 80 °C. This plasma-free ULT-ALD eliminates the damage to the HgCdTe surfaces due to plasma and high temperature. The capacitance–voltage characteristics of metal–insulator–semiconductor (MIS) structures based on HgCdTe with traditional CdTe/ZnS and ULT-ALD ZnS passivation are studied. The fixed charge surface density at the interface of MIS structures passivated by ALD ZnS was −6.40 × 1011 cm−2, Lower than the value of double-layer passivation 4.20 × 1012 cm−2, and the density of slow states is 5.94 × 1011 cm−3 and 2.61 × 1012 cm−3 respectively. The hysteresis of the MIS structure with ALD ZnS passivation is almost unchanged with temperature. From these findings, combined with characteristics of high density and conformality of ALD films, we conclude that ALD ZnS has better electrical properties than traditional double layer passivation provides significantly improved interface quality, but obtained density of fixed charge is still quite high and should be further reduced.

Influence of passivation layer on thermal stability of Nb:TiO2−x samples for shutter-less infrared image sensors

Test devices of unpassivated, single-layer passivated, and double-layer passivated samples were fabricated to analyze the enhancement of thermal stability for shutter-less infrared (IR) image sensors. In this study, double-layer passivation (SiOx/SiNx) was proposed to avoid the oxygen-diffusion from unpassivated or single-layer (SiOx) passivated Nb:TiO2−x (TNO) samples. Before fabricating the test device, high-temperature (450 °C) annealing was carried out under oxygen-rich ambient conditions to improve the thermal stability by reducing the number of oxygen vacancies in the as-deposited TNO samples. The double-layer passivated sample showed higher thermal stability than the other samples. The structural and bolometric properties were also studied for all passivated samples and the obtained results attested that the properties seemed to be almost similar for different passivation layers. It was found that the proposed double-layer passivated TNO sample could provide enhanced thermal stability for future shutter-less IR sensors.

Small pyramidal textured ultrathin crystalline silicon solar cells with double-layer passivation.

Ultrathin crystalline silicon solar cells are a promising technology roadmap to achieve more cost effectiveness. However, experimental reports on ultrathin crystalline silicon cells with thickness less than 20 µm are rare. Here, we experimentally fabricate and investigate ultrathin monocrystalline silicon solar cells consisting of 16 µm-silicon base thickness and low-cost front random pyramidal texture with the feature size of 1-2 µm. The normalized light absorption is calculated to explain the measured external quantum efficiency. The achieved efficiency is 15.1% for the single-layer passivated textured solar cell. In addition, via double-layer passivation of Al2O3/SiNx, the efficiency is further increased to 16.4% for the best textured cell, which significantly improves the absolute efficiency with Δη = 1.3%.

Development of Passivated Heterogeneous Metal Nanogaps Using E-Beam Overlay Techniques

We present a planar nanogap structure with heterogeneous metal electrodes separated by a distance of tens of nanometers. This asymmetric nanodevice is meant for metal/molecule/metal transport analysis. The heterogeneous aspect of the metal electrodes is meant to trigger the assembly orientation of selected molecules across the gap. With E-beam overlay technique and double-layer passivation, the structure has a well-defined and reproducible gap and shows good chemical durability and dielectric properties.

Improvement in the ability to block Hg out diffusion from Hg1−xCdxTe by hydrogenation

Hydrogenation and double-layer passivation of mercury cadmium telluride (Hg1−xCdxTe or MCT) is studied and compared with passivation by a single CdTe layer. Two different passivated structures, namely CdTe/hydrogenated MCT and ZnS/CdTe/MCT, are investigated using Rutherford backscattering spectroscopy. No significant improvement in the compositional profile of CdTe/MCT is seen in a doubly passivated ZnS/CdTe/MCT structure, i.e. the presence of a ZnS passivating layer does not improve the compositional profile in CdTe/MCT structures. Similar to the CdTe/MCT sample, ZnS/CdTe/MCT was also found to have a 35 nm thick interlayer mixing region between CdTe and MCT. In CdTe/hydrogenated MCT the interface is found to be sharp and suggests complete blockage of Hg out diffusion by hydrogenation, and it is also observed that CdTe/hydrogenated MCT preserves its effectiveness in preventing the Hg out diffusion even after annealing at 80 °C in a vacuum. This improvement may be due to restriction of Hg vacancy diffusion by hydrogenation.

Thermal Stability in HgCdTe IR Photodiodes

ABSTRACTPackaging of HgCdTe photodiode detector arrays in a dewar involves degassing at elevated temperatures for several days so as to achieve vacuum integrity. This sustained exposure to relatively high temperatures can influence the HgCdTe bulk material properties, p-n junction integrity, and the passivant-HgCdTe interface. This work investigates the effects of bake-out treatment on the performance of HgCdTe based photodiodes formed using a new plasma induced type conversion process. Experimental results of a series of experiments in both long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) devices are presented.Bulk lifetime was used as an indicator of the change in the bulk material resulting from baking in vacuum and was measured by photoconductive decay. These measurements did not show any appreciable changes as a result of baking. Modification of the doping profile in the n-p junction may also result from high temperature baking. Doping profiles of the photodiodes were studied by measuring the junction capacitance-voltage relation before and after baking. The results of these tests after baking showed no changes to C-V measurements from those before bake.The effect of baking on the passivant/HgCdTe interface was also examined by carrying out surface recombination velocity measurements by photoconductive decay on samples with different passivation layers.Variable area HgCdTe photodiodes have also been fabricated and studied to understand the effect of the surface condition of the performance of the devices. Initial bake tests on LWIR devices show that the technology is stable when employing a double layer passivation technique. Bake tests on the more advanced MWIR technology indicates that the plasma induced type conversion process produces stable photodiodes with state of the art performance.

SiNx :H/SiO2 Double-Layer Passivation With Hydrogen-Radical Annealing For Solar Cells

A SiNx :H/SiO2 double-layer structure as the passivation layer and hydrogen-radical post annealing were introduced to decrease the surface recombination velocity on crystalline silicon. Effective lifetime was much increased by introducing a SiNx :H/SiO2 double-layer passivation structure instead of a SiNx :H or SiO2 single-layer, while the hydrogen radical post annealing improves the interface characteristics more effectively than N2 annealing. The results of C–V measurement suggest that many positive charges exist in the SiNx :H layer. The combination of field effect by these charges and the decrease of SiO2/c-Si interface defects by hydrogen-radical annealing effectively decrease the surface recombination velocity.