Si／SiGe／Si HBT的优化设计

给出了常温和低温Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ的设计原则，并进行了讨论。指出了低温和室温ＨＢＴ设计上的差异。这些原则可用于设计特定要求的Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ。     

Hierarchical polypyrrole encapsulating Bi2O4 to enhance charge separation and light absorption with boosted visible light photocatalytic activity

Bi₂O₄, as a typical visible-light responsive photocatalyst (band gap～ 2.0 eV), has aroused enormous attention in recent years. However, single Bi₂O₄ has the problem of high recombination probability of photogenerated electron-hole pairs, which inevitably hampers its photocatalytic performance. Herein, hierarchical polypyrrole encapsulated Bi₂O₄(Bi₂O₄@PPy) has been constructed via an in-situ vapor-phase polymerization method, producing PPy tightly coated Bi₂O₄ core-shell structure photocatalyst. Thanks to this full coating and hierarchical structure, the charges separation efficiency, and the light absorption capacity of Bi₂O₄@PPy hybrid are promoted, leading to obviously enhanced visible light photocatalytic activity. The optimal Bi₂O₄@PPy composite could be obtained through controlling the polymerization time for 9 h, whose catalytic activity is as 2.43 times as that of Bi₂O₄ alone. The active species trapping experiments suggest that holes play a vital role in the photocatalytic degradation process. A plausible reaction mechanism over the Bi₂O₄@PPy hybrid photocatalyst is also proposed based on the characterization and experimental results.     

Effect of edges on the reliability of GaAs and (AlGa) as heterojunction leds

The effect of various diode geometries on the degradation rate of heterojunction diodes with either GaAs or (AlGa)As in the recombination region has been studied. It is shown that GaAs diodes are particularly sensitive to edge-related degradation which varies with the current density J as J^3/2. The addition of Al to the recombination region considerably reduces the degradation rate of diodes both with and without exposed edges, and data are reported for Al_0.1Ga_0.9As stripe-contact edge-emitting structures operating for over 20,000 hours with no change in output at 1000 A/cm².     

InGaAs/InGaAsP/InP SAGM-APD器件设计考虑及I_P—V曲线二级阶梯状扭折

本文根据雪崩电场和限制隧道电流电场要求出发,设计和估算了InGaAs/InGaAsP/InPSAGM-APD器件参数,测量并解释了I_p-V曲线的二级阶梯扭折行为,指出了V_(th)/V_B以1/3左右为宜和与实际测量的M_p比较吻合的经验公式。     

Heterojunction solar cells of SnO2/Si

Heterojunction solar cells (HJSC’s), fabricated by electron beam evaportaion of SnO₂ films onto monocrystalline and polycrystalline Si substrates, show conversion efficiencies as high as 9.9%, fill factors of 0.64, and open circuit voltages of 525 mV under AMI simulated irradiation. The SnO₂, an n-type semiconductor, acts as a transparent window to solar irradiation and as an antireflection coating of the Si, and it provides the band bending in the Si necessary for photovoltaic conversion. The SnO₂ films, nominally 50 nm thick, have conductivities of the order of 10³(Ω-cm)⁻¹ so that the film makes a good electrical contact between the junction and the metallic front contacts. Measurements of C⁻²-V and I-V characteristics are consistent with heterojunction theory, and the data imply an electron affinity of the SnO₂ of approximately 0.8 eV greater than the electron affinity of Si. This value limits the open circuit voltage of HJSC’s made on p-type substrates to values too small for useful photovoltaic conversion. The predominant dark current mechanism of units of n-type substrates at room temperature and forward bias in the range of 0.3−0.5 V is electron-hole recombination in the transition region. The experimentally determined activation energy is 0.51 eV, approximately E_g/2. At forward voltages below 0.3 V, multistep tunneling via interband states predominates. The photocurrent apparently depends on interface states through which the photogenerated holes in the Si recombine with electrons in the SnO₂.     

Evaluation of InP-to-silicon heterobonding

In this paper, we evaluate hydrophilic (HP) and hydrophobic (HB) surface pre-treatments in InP-to-Si direct wafer bonding. Surface roughness and surface chemistry was examined using atomic force microscopy and X-ray photoelectron spectroscopy, respectively. After bonding, the bonded interfaces were evaluated using infrared transmission imaging, bond-strength and current–voltage (I–V) measurements. It was found that HP surface treatment using oxygen plasma makes room temperature bonding of InP and Si very spontaneous, and results in high bond-strengths already after low-temperature annealing. This was not observed when using standard oxidising acids as HP surface treatment before bonding. HB InP and Si surfaces, also, did not prove to bond spontaneously at room temperature and the bond-strength started to increase only after annealing at about 400°C. HB bonding and annealing at 400°C was though the best choice regarding the electrical characteristics of the bonded InP/Si heterojunction.     

Modelling of SiGe heterobipolar transistors: 200 GHz frequencies with symmetrical delay times

Our basic approach is to develop a symmetrical design with equal delay times for collector, base and the total load to simulate the high frequency behaviour of SiGe heterobipolar transistors (HBTs). On this base we have investigated the feasibility of SiGe HBTs with transit frequencies f_T above 200 GHz. A symmetrical design reaching f_T=208 GHz is presented. The dependence of the high frequency behaviour on Ge content and vertical transistor design is shown. Critical parameters like the maximum current density and the breakthrough voltage are considered. An analytical model is compared to numerical simulations and experimental data.     

Simplified Method of Valence Band Offset Calculation at Strained Layer Heterojunction

The average bond energy method is popularized and applied to study band offsets at strained layer heterojunctions.By careful examination of hydrostatic and uniaxial strain actions on the band offset parameter Emv,it is found that the average band offset parameter Emv,av=Em-Ev,av remains basically unchanged under different strain conditions.Therefore,provided the band offset parameter before strain Emv,0 of bulk material is calculated,and the experiment values of deformation potential b and spin-orbit(SO)splitting energy △0 are quoted,the Emv at strained layer can be obtained by a simple and convenient algebraic calculation.Thus the valence band offset △Ev at strained layer heterojunctin can also be predicted conveniently.This simplified calcultation method is characterized by decreased calculation amount and increased conviction due to use as many as possible the experiment values.     

Evaluation of bis-dicyanovinyl short-chain conjugated systems as donor materials for organic solar cells

Three conjugated compounds based on carbazole, cyclopentadithiophene and dithienopyrrole substituted by branched alkyl chains have been synthesized by the Knoevenagel condensation of malonodinitrile with the appropriate dicarboxaldehyde. Electronic properties of the target compounds have been analyzed in solution by UV-vis absorption spectroscopy and cyclic voltammetry and their potentialities as a donor material in donor-acceptor heterojunction solar cells have been evaluated in bilayer devices involving both solution processed or vacuum deposited donor layers and thermally evaporated fullerene C₆₀ as an acceptor.     

In2Se3/CdS nanocomposites as high efficiency photocatalysts for hydrogen production under visible light irradiation

Hydrogen energy is an important clean energy. Using visible light to produce hydrogen by semiconductor photocatalysts is one of the current research hotspots. In this work, In₂Se₃/CdS nanocomposite photocatalysts with different mass content of CdS are prepared. The In₂Se₃/CdS photocatalyst with 85.25% CdS mass content exhibits the optimal photocatalytic hydrogen evolution activity (1.632 mmol g^?1 h^?1), which is much higher than that of CdS (0.715 mmol g^?1 h^?1) and In₂Se₃ (trace). Moreover, the In₂Se₃/CdS photocatalyst still maintains a high hydrogen evolution rate after five cycles. The high photocatalytic activity and stability of the In₂Se₃/CdS nanocomposite is due to the formation of heterojunction between In₂Se₃ and CdS. The existence of heterojunction is confirmed by high resolution transmission electron microscopy image and X-ray photoelectron spectra. Theoretical calculations and experimental results indicate that the electron transfer route at the heterojunction is step-scheme. The step-scheme helps the separation of photogenerated electrons and holes, and maximize the hydrogen evolution activity. This work provides a high efficiency step-scheme photocatalyst for hydrogen production.