Hailing Li

Transport through a Si single-electron transistor

A Si single-electron transistor with in-plane point contact metal gates is fabricated by a self-aligned process. The in-plane gates are used to squeeze the channel and to form a single dot at the constriction of the channel. A few dips are observed in the characteristic of the drain current versus the top gate voltage for a device with a 70 nm wide channel. This is attributed to the stochastic Coulomb blockade within the multiple-dot structure.

The effect of saw mark on the over-ghosting for acidic textured multicrystalline wafers with silicon nitride anti-reflectance films

The use of light-induced plating (LIP) for metallization of solar cells is attractive because of its potential simplicity in that the current driving the metal reduction process is derived from the solar cell under illumination. However, there is a challenge when applying the LIP techniques on standard acidic textured multicrystalline silicon wafers with a silicon nitride coated surface. The over-plating can cause the decrease of the solar cells efficiency mainly through the shunt or forming schottky contact, and shading losses. The main reason of over-plating on acidics, also on the alkali textured multicrystalline silicon wafers is saw mark. The over-plating on saw-damage multicrystalline silicon is still evident even the coated SiNx:H films is proper to as the plating mask. In this work, the effect of saw marks on over-plating are examined and evaluated. Finally, the elimination of over-plating on acidic textured multicrystalline silicon cells are demonstrated

Preparation of p+-layers using water vapour as oxidant in BBr3 diffusion for silicon solar cells

A boron diffusion process using water vapour as oxidant mixed with oxygen is introduced. Boron-doped emitter sheet resistances ranging from 30 to 400 Ω/sq and saturation current densities as low as 100 to 300 fA cm−2 for Al2O3/SiNx passivated emitters were achieved. For the predeposition process using water vapour, a low sheet resistance of 20 Ω/sq with uniformity of 5%, and a high sheet resistance of 100 Ω/sq with good in-wafer and wafer-to-wafer uniformities within 10% were achieved. With wet-oxygen predeposition method, an open-circuit voltage of 680 mV and pseudo fill factor (pFF) of 81% were obtained for the Al2O3 double-sides passivation p+/n-Si structure by the measurement of Suns-Voc. These results indicate that water vapour was suitable for forming both p+-emitters and back-surface fields for highly efficient n- and p-type solar cells.

Improved Reflectance for Textured Mc-Silicon Solar Cells by SF6/O2 Plasma Etching

On account of enhancing surface light trapping by reducing reflectance, front surface texturiing is always a key to improve the solar cells performance. As a maskless plasma texturing technique, reactive ion etching using SF6/O 2 plasma brings down reflectance distinctly by fluorine ions etching the surface of mc-silicon solar cells with the assisting of O2. The textured surface with bowl-like nanostructure exhibits fine anti-reflectance effect. Optimal reflectance of mc-silicon solar cells could be obtained by adjusting gases flow ratios, plasma power and etching time.

Resonant tunneling through energy states of InAs quantum dots in GaAs metal–semiconductor diode structures

Abstract Direct electronic transport properties in a GaAs metal–semiconductor diode structure containing InAs self-assembled quantum dots are reported. Current peaks and negative differential resistance due to resonant tunneling through the zero-dimensional states of the InAs dots are clearly observed under reverse biases. The second derivative of the current versus voltage shows more structures at larger voltages, which are attributed to the resonant tunneling through the excited states of the quantum dots. From the peak positions in the second derivative, the energy separations between the states of the quantum dots are roughly estimated according to a simple calculation based on our experimental data.

3-D Solar Cells Based on Radial Silicon Heterojunctions Exploiting Microhole Lattices

In this letter, 3-D solar cells based on radial amorphous/crystalline silicon heterojunctions (SHJs), which are formed on 2-D lattices of vertical high aspect-ratio microholes (MHs) etched in crystalline silicon (c-Si) substrates, are realized with conversion efficiency of ~ 3%. Silicon high aspect-ratio MH lattices, with hole diameter of a few micrometers and hole depth of tens micrometers, are produced on n-type c-Si substrates by electrochemical micromachining (ECM) technology with low reflectance ( depending on diameter and depth) in the wavelength range between 400 and 900 nm, which is commonly exploited for solar cell application. The radial SHJ solar cells are obtained by successive quasi-conformal deposition of hydrogenated amorphous silicon (a-Si:H) i-layer and p-layer, respectively, via plasma-enhanced chemical vapor deposition at 200°C, within the MH lattices, and subsequent indium tin oxide and Ag deposition for the formation of electrical front and back contacts, respectively. Experimental conversion efficiencies up to 2.72% are obtained under standard AM1.5 illumination with intensity of 100 mW/cm2, thus envisaging that ECM technology can be successfully adopted to realize efficient 3-D solar cells based on radial p-n junctions exploiting high aspect-ratio MH lattices, in particular, or other microstructures, in general.

A New Attempt at Alkaline Texturization of Monocrystaline Silicon with Anionic Surfactant as the Additive

Owing to the volatilization of isopropanol (IPA), instability in the alkaline texturization of monocrystalline silicon has been a big problem for a long time. Many additives were adapted to replace IPA, such as high boiling point alcohols. In this experiment, as a new attempt, sodium lauryl sulfate (SDS), a type of anionic surfactant, was used as the additive in NaOH solution. The etching properties of silicon in 2 wt % NaOH/15–30 mg/L SDS solution were analyzed. To improve the wettability of silicon, two types of metal salt, NaCl and Na2CO3 with concentration from 2 to 15 wt %, were applied to the 2 wt % NaOH/15 mg/L SDS solution. The results showed that the effect of NaCl was better than that of Na2CO3. Finally, the role of the additive was discussed.

Calculated and experimental research of sheet resistances of crystalline silicon solar cells by dry laser doping

In this paper, the calculated and experimental research of sheet resistances of crystalline silicon solar cells by dry laser doping is investigated. The nonlinear numerical model on laser melting of crystalline silicon and liquid-phase diffusion of phosphorus atoms by dry laser doping is analyzed by finite difference method implemented in MATLAB. The calculated sheet resistances as a function of laser energy density is obtained and the calculated results are in good agreement with the corresponding experimental measurement.

Hysteresis in electronic transport through an ensemble of InAs self-assembled quantum dots

Abstract We have observed pronounced hysteresis loops in current transport measurements in metal–semiconductor–metal diode with InAs self-assembled quantum dots. The charging and discharging of the quantum dots induced the hysteresis. By sweeping the voltage the dots could be charged and discharged. We found that the tunneling rate of the electrons from the dots dominated the discharging process and that the forward current flowing through the quantum dots layer from the GaAs to metal contact controlled the charging process. Our theoretical calculation shows that the electrons trapped in the ground states of the quantum dots give rise to the charging effect, rather than those trapped in the excited states.