Ding Wuchang

Optimization of Al2O3/SiNx stacked antireflection structures for N-type surface-passivated crystalline silicon solar cells

In the case of N-type solar cells, the anti-reflection property, as one of the important factors to further improve the energy-conversion efficiency, has been optimized using a stacked Al2O3/SiNx layer. The effect of SiNx layer thickness on the surface reflection property was systematically studied in terms of both experimental and theoretical measurement. In the stacked Al2O3/SiNx layers, results demonstrated that the surface reflection property can be effectively optimized by adding a SiNx layer, leading to the improvement in the final photovoltaic characteristic of the N-type solar cells.

Antireflection properties and solar cell application of silicon nanostructures

Silicon nanowire arrays (SiNWAs) are fabricated on polished pyramids of textured Si using an aqueous chemical etching method. The silicon nanowires themselves or hybrid structures of nanowires and pyramids both show strong anti-reflectance abilities in the wavelength region of 300–1000 nm, and reflectances of 2.52% and less than 8% are achieved, respectively. A 12.45% SiNWAs-textured solar cell (SC) with a short circuit current of 34.82 mA/cm2 and open circuit voltage (Voc) of 594 mV was fabricated on 125 × 125 mm2 Si using a conventional process including metal grid printing. It is revealed that passivation is essential for hybrid structure textured SCs, and Voc can be enlarged by 28.6% from 420 V to 560 mV after the passivation layer is deposited. The loss mechanism of SiNWA SC was investigated in detail by systematic comparison of the basic parameters and external quantum efficiency (EQE)of samples with different fabrication processes. It is proved that surface passivation and fabrication of a metal grid are critical for high efficiency SiNWA SC, and the performance of SiNWA SC could be improved when fabricated on a substrate with an initial PN junction.

Optimization of ohmic contact for InP-based transferred electronic devices

The effect of the annealing time and annealing temperature on Ni/Ge/Au electrode contacts deposited on the n-type InP contact layer has been studied using a circular transmission line model. The minimum specific contact resistance of 3.2 × 10−7 Ωcm2 was achieved on the low-doped n-type InP contact layer with a 40 s anneal at 425 °C. In order to improve the ohmic contact and reduce the difficulty in the fabrication of the high doped InP epi-layer, the doping concentration in the InP contact layer was chosen to be 5 × 1018 cm−3 in the fabrication of transferred electronic devices. Excellent differential negative resistance properties were obtained by an electron beam evaporating the Ni/Ge/Au/Ge/Ni/Au composite electrode on an InP epi-layer with a 60 s anneal at 380 °C.

A comparison of silicon oxide and nitride as host matrices on the photoluminescence from Er3+ ions

This paper compares the properties of silicon oxide and nitride as host matrices for Er ions. Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system. After deposition, the films were implanted with Er3+ at different doses. Er-doped thermal grown silicon oxide films were prepared at the same time as references. Photoluminescence features of Er3+ were inspected systematically. It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe. However, a very high annealing temperature up to 1200 degrees C is needed to optically activate Er3+ which may be the main obstacle to impede the application of Er-doped silicon nitride.

f T = 260 GHz and f max = 607 GHz of 100-nm-gate In0.52Al0.48As/In0.7Ga0.3As HEMTs with G m.max = 1441 mS/mm*

The 100-nm T-gate InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) with the width of 2 × 50 μm and source-drain space of 2.4 μm are systematically investigated. High indium (In) composition of InGaAs layer was adopted to acquire the higher mobility of the channel layer. A sandwich structure was adopted to optimize the cap layers and produce a very low contact resistance. The fabricated devices exhibit extrinsic maximum transconductance G m.max = 1441 mS/mm, cutoff frequency f T = 260 GHz, and maximum oscillation frequency f max = 607 GHz. A semi-empirical model has been developed to precisely fit the low-frequency region of scattering parameters (S parameters) for InP-based HEMTs. Excellent agreement between measured and simulated S parameters demonstrates the validity of this approach.

Improving poor fill factors for solar cells via light-induced plating

Silicon solar cells are prepared following the conventional fabrication processes, except for the metallization firing process. The cells are divided into two groups with higher and lower fill factors, respectively. After light-induced plating (LIP), the fill factors of the solar cells in both groups with different initial values reach the same level. Scanning electron microscope (SEM) images are taken under the bulk silver electrodes, which prove that the improvement for cells with a poor factor after LIP should benefit from sufficient exploitation of the high density silver crystals formed during the firing process. Moreover, the application of LIP to cells with poor electrode contact performance, such as nanowire cells and radial junction solar cells, is proposed.

Photoluminescence spectroscopy of sputtering Er-doped silicon-rich silicon nitride films

Er-doped silicon-rich silicon nitride (SRN) films were deposited on silicon substrate by an RF magnetron reaction sputtering system. After high temperature annealing, the films show intense photoluminescence in both the visible and infrared regions. Besides broad-band luminescence centered at 780 nm which originates from silicon nanocrystals, resolved peaks due to transitions from all high energy levels up to 2H11/2 to the ground state of Er3+ are observed. Raman spectra and HRTEM measurements have been performed to investigate the structure of the films, and possible excitation processes are discussed.

High performance oscillator with 2-mW output power at 300 GHz

Material structures and device structures of a 100-GHz InP based transferred-electron device are designed in this paper. In order to successfully fabricate the Gunn devices operating at 100 GHz, the InP substrate was entirely removed by mechanical thinning and wet etching. The Gunn device was connected to a tripler link and a high RF (radio frequency) output with power of 2 mW working at 300 GHz was obtained, which is high enough for applications in current military electronic systems.

Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors

With consideration of the modulation frequency of the input lightwave itself, we present a new model to calculate the quantum efficiency of RCE p-i-n photodetectors (PD) by superimposition of multiple reflected lightwaves. For the first time, the optical delay, another important factor limiting the electrical bandwidth of RCE p-i-n PD excluding the transit time of the carriers and RCd response of the photodetector, is analyzed and discussed in detail. The optical delay dominates the bandwidth of RCE p-i-n PD when its active layer is thinner than several 10 nm. These three limiting factors must be considered exactly for design of ultra-high-speed RCE p-i-n PD.

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55 μm: physics, design and simulation

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30 mu m could absorb 90% of the incident light at 1.55 mu m wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.