Jiakun Liu

Saturation of the light‐induced defect density in hydrogenated amorphous silicon

We report new experimental results on the saturation of the light‐induced defect density in hydrogenated (and fluorinated) amorphous silicon. The films were illuminated near room temperature up to 5000 h with bandpass filtered red light at a carrier generation rate G of 5×1020 cm−3 s−1, or up to 20 h with Kr+ laser light (λ=647.1 nm) at G=3×1022 cm−3 s−1. The bulk defect densities Ns saturate in both cases in the vicinity of 1017 cm−3. The saturation values are almost independent either of G or of temperature in the range from room temperature to about 70 °C. The illumination time to reach saturation is approximately proportional to 1/G2. These results are discussed within the framework of existing models for the light‐induced defects.

OPTOELECTRONIC PROPERTIES OF HYDROGENATED AMORPHOUS SILICON FILMS DEPOSITED UNDER NEGATIVE SUBSTRATE BIAS

We present a detailed study of the effects of ion bombardment on the optoelectronic properties of a‐Si:H films. Two series of samples were deposited from a rf glow discharge at 30 and 100 mTorr of silane pressure, corresponding to two different deposition conditions. The energy of the ions impinging on the substrate was increased by applying a negative dc bias in steps of 25 V to the substrate holder. The increase of the substrate bias from 0 to −100 V had no effect on the deposition rate of a‐Si:H at 30 mTorr, whereas a factor of 2 decrease was observed for deposition at 100 mTorr. The density of states of the a‐Si:H films, determined by photothermal deflection spectroscopy and by the constant‐photocurrent method, decreased as the substrate bias was increased up to −50 V, especially for the series deposited at 100 mTorr. At the same time the valence‐band tail became sharper. These observations are consistent with the improvement of the electron drift‐mobility deep‐trapping‐lifetime (μdτd)e product, deter...

Interior C 2,alpha regularity for potential functions in optimal transportation

In this paper we study the continuity of second derivatives of solutions to the Monge–Ampère equation arising in optimal transportation. We obtain Hölder and more general continuity estimates for second derivatives, when the inhomogeneous term is Hölder and Dini continuous, together with corresponding regularity results for potentials.

Dependence of the saturated light‐induced defect density on macroscopic properties of hydrogenated amorphous silicon

We report a study of the saturated light‐induced defect density Ns,sat in 37 hydrogenated (and in part fluorinated) amorphous silicon [a‐Si:H(F)] films grown in six different reactors under widely different conditions. Ns,sat was attained by exposing the films to light from a krypton ion laser (λ=647.1 nm). Ns,sat is determined by the constant photocurrent method and lies between 5×1016 and 2×1017 cm−3. Ns,sat drops with decreasing optical gap Eopt and hydrogen content cH, but is not correlated with the initial defect density Ns,ann or with the Urbach tail energy Eu. We discuss our results within the framework of existing models for light‐induced defects.

On the uniqueness of Lp-Minkowski problems: The constant p -curvature case in R3

Abstract We study the C 4 smooth convex bodies K ⊂ R n + 1 satisfying K ( x ) = u ( x ) 1 − p , where x ∈ S n , K is the Gauss curvature of ∂ K , u is the support function of K , and p is a constant. In the case of n = 2 , either when p ∈ [ − 1 , 0 ] or when p ∈ ( 0 , 1 ) in addition to a pinching condition, we show that K must be the unit ball. This partially answers a conjecture of Lutwak, Yang, and Zhang about the uniqueness of the L p -Minkowski problem in R 3 . Moreover, we give an explicit pinching constant depending only on p when p ∈ ( 0 , 1 ) .

Amorphous silicon-germanium thin-film photodetector array

The authors report a photodetector array based on an amorphous silicon-germanium alloy thin film. The detector array is designed for detecting light pulses from (Ga,Al)As laser diodes. An experimental 2*2 detector array, addressed by a silicon shift register, works to a clock frequency of 25 MHz and shows good stability.<<ETX>>

Substrate temperature dependence of the growth kinetics and opto-electronic properties of a-Si:H films deposited by RF glow discharge☆

Abstract We report the effects of the substrate temperature T s on the growth kinetics and the opto-electronic properties of a-Si:H films deposited by rf glow discharge. In the low rf power regime, we observe an increase of the a-Si:H deposition rate and a decrease of the a-Si:H work function as we increase the substrate temperature. Moreover, the density of bulk defect states shows a broad minimum as a function of T s . In particular, a-Si:H films with defect densities as low as 2×10 15 cm −3 can be deposited at 150°C. However, preliminary light-soaking experiments show that light-induced degradation is stronger for a-Si:H deposited at lower T s .

Growth‐induced surface state in hydrogenated and fluorinated amorphous silicon

The steady‐state density of surface states during the deposition of hydrogenated and fluorinated amorphous silicon (a‐Si:H,F) can be adjusted via the deposition parameters, particularly the growth pressure. The density of surface states can be frozen in if the sample is cooled immediately after the termination of growth. We have measured frozen in densities of surface states between 1.5×1012 cm−2 and 4×1014 cm−2. a‐Si:H,F grown at high density of surface states exhibits a small Urbach energy and a low bulk defect density.

A Multiagent-Based Domain Transportation Approach for Optimal Resource Allocation in Emergency Management

In metropolitan regions, emergency events request urgent response within a short time limit in order to minimise the damage and the number of fatality. Most of these events require different resources that are usually distributed over a large area. How to efficiently allocate the distributed resources to an event is a challenging research issue. Traditional centralised resource allocation approaches have difficulties to find out the best resource assignment within the event’s time limits by considering the dynamics of the metropolitan environment and the event itself. In this paper, a multiagent-based decentralised resource allocation approach using domain transportation theory is proposed to handle an emergency event with multiple tasks. Experimental results indicates that the proposed approach can effectively generate the optimal resource allocation plans by considering multiple factors of an emergency event.

Dual-beam photocurrent spectra in undoped a-Si:H : anomalous band, optical transition energy, and correlation energy

Abstract It is shown that the anomalous band in dual-beam CPM (DBCPM) spectra of a-Si:H results from a combination of two processes: photocurrent enhancement due to excitations by the probe light from the valence band to the D+ states, and photocucurrent reduction due to excitations by the probe light from the D0 states to the conduction band. Using the DBCPM spectra, we measured the optical transition energy (0.77 eV) and the electron correlation energy (0.16 eV) for the filled D− defects.