Calculation of external circuit current of thin-film semiconductor structures

The expression for the external circuit current for thin-film semiconductor structures is derived. A connection of the external current with the normal modes in the semiconductor film is ascertained.     

A closed-form trapped-charge-included drain current compact model for amorphous oxide semiconductor thin-film transistors

A closed-form drain current compact model for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs), including the influence from trapped charges, is presented in this paper. Accounting for both channel and interface trapped charges in this model, we explicitly solve the inherent closed-form surface potential by improving the computational efficiency of the effective charge density approach. Furthermore, based on the explicit solution of the surface potential, the expressions of the trapped and inversion charges in the channel film are derived analytically, and the drain current is integrated from the charge sheet model. Then, for the cases of the different operational voltages, the accuracy and practicability of our model are verified by numerical results of the surface potential and experimental data of the drain current in amorphous In-Ga-Zn-O TFTs, respectively. Finally, we give a discussion about the influence of the interface trapped charges on the device reliability. As a result, the model can be easily to explore the drain current behavior of the AOS TFTs for next-generation display circuit application.     

Bulk switching of an amorphous semiconductor

Bulk switching of a Si3Ge4As38Te55amorphous semiconductor is reported. Even though the contacts are separated by 1 mm, a delay time of only 10 µs is observed. This is attributed to an active region of only 0.1-mm thickness near the positive electrode. The threshold voltage is 250 volts at room temperature.     

Transient temperature rise in silicon semiconductor devices

The temperature rise in silicon devices under pulsed power conditions is calculated by a numerical method which takes into account the nonlinear properties of the materials. Power is assumed to be dissipated in a thin but finite layer at the surface of a one-dimensional structure. The effect of various types of heat sinks on the peak temperature rise is shown.     

Transient effects in external cavity semiconductor lasers

In several important applications of external cavity operated semiconductor lasers, including studies for FM optical communication and frequency stabilized lasers for coherent communication systems, the transient response of the laser is of crucial importance. In this letter, we present a first study of the transient optical response following a step current excitation applied to an AlGaAs laser operating in a dispersive external cavity. The study shows for the first time that, for optical feedback near the gain peak of the laser, a steady state is reached after only three roundtrips in the external cavity. However, for optical feedback far (∼100 Å) from the gain peak, 20 or more roundtrips are required before a steady state can be reached. It is also shown that under certain operation conditions the optical feedback can induce damped relaxation oscillations at each subsequent roundtrip in the external cavity.     

Electron beam heating in amorphous semiconductor beam memory

The high-speed electron beam heating and the subsequent cooling processes in an amorphous semiconductor target of a beam memory have been studied by computer simulation. Such a memory would utilize the amorphous and the crystalline phases of chalcogenide thin films as the binary states of the memory. For an electron source of 1-µ radius, the results suggest that a storage target, consisting of a chalcogenide thin film whose thickness is twice the electron penetration range on a good heat sinking substrate, is the optimum target configuration. Possible high-speed memory operating characteristics with present long-life high-brightness electron guns are described.     

Anomalous Kossel effect in semiconductor structures

A theoretical analysis is made of the intensity distribution within a Kossel line from a semiconductor crystal in an extremely asymmetric x-ray diffraction scheme. Crystals of thickness comparable with the x-ray penetration depth are evaluated as a potential means of bringing about the anomalous Kossel effect, which is predicted to occur in the vicinity of a degenerate point. The possibility is investigated of using a thin amorphous film to enhance the effect. Dispersion-surface geometry, excitation points, and Poynting-vector directions are examined in detail for the anomalous Kossel effect.     

Optical bistability in semiconductor periodic structures

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon     

Self-heating effects in basic semiconductor structures

Investigates the effects of self-heating on the high current I -V characteristics of semiconductor structures using a fully coupled electrothermal device simulator. It is shown that the breakdown in both resistors and diodes is caused by conductivity modulation due to minority carrier generation. In isothermal simulations with T=300 K, avalanche generation is the source of minority carriers. In simulations with self-heating, both avalanche and thermal generation of minority carriers can contribute to the breakdown mechanism. The voltage and current at breakdown are dependent on the structure of the device and the doping concentration in the region with lower doping. For all structures, except highly doped resistors with poor heating sinking at the contacts, the temperature at thermal breakdown ranged from 1.25T_i to 3T_i , where T_i is the temperature at which the semiconductor goes intrinsic. Hence, it is found that T=T_i is not a general condition for thermal (or second) breakdown. From these studies, an improved condition for thermal breakdown is proposed     

Spontaneous emission in multilayer semiconductor structures

A theoretical analysis of spontaneous emission from a quantum well in dielectric multilayer structures, especially the influence of dielectric geometry on the relative intensities of guided and radiation modes and on polarization, is presented. We first discuss a relatively simple three-layer case, and subsequently a technologically more interesting five-layer structure that has been proposed for a high-power laser. The expression for the partial as well as total, emission rates is derived within a broader framework of coupled Heisenberg equations of motion for charge carriers and the quantized electromagnetic field. Thereby, the explicit mode decomposition of the Green tensor is avoided. Still, the beta factor for individual guided modes, which is a relevant quantity for the lasing threshold of a device, can be identified and a competition between modes is shown to exist in specific cases     

Radiative efficiency in low-dimensional semiconductor structures

The ratio of the spontaneous emission and Auger recombination rates for quantum wells and wires is compared theoretically with that for bulk structures. Dramatic improvements in radiative efficiency are not predicted for these novel structures unless carrier densities are greatly reduced.     

Pre-threshold conductance and polarization effects in amorphous semiconductor switches

It is shown that the conductance and threshold parameters of threshold switches depend on the manner in which switching systems are addressed. Slow voltage ramps lead to internal polarization; fast square pulses do not. The polarization processes influence all switching operations performed sequentially; their room-temperature relaxation time is of the order of several milliseconds. The observations are interpreted on the basis of a space charge model involving injected carriers, subsequently trapped.     

Transient photocurrent and photoluminescence in porous silicon

Transient photocurrent in porous silicon samples subjected to prolonged storage in air has been studied using the time-of-flight technique at temperatures in the range 300–350 K and electric field strengths of 10⁴–10⁵ V/cm. Photoluminescence has been studied in the same samples at T=300 K using time-resolved spectroscopy. A conclusion is made on the basis of comparison of the data obtained that localized states play important part in both the processes at characteristic times of these processes falling within the microsecond range.     

Electron-optical masking of semiconductor structures

Electron-optical techniques were employed to fabricate planar silicon transistors having a 1-micron strip width and a combined dimensional and registration tolerance of 1000 Å. A new electron-sensitive positive resist was used to define a conventional oxide diffusion mask. The exposure equipment is described and electrical parameters of the complete device are given.     

Size-quantization stark effect in quasi-zero-dimensional semiconductor structures

A theory of the size-quantization Stark effect in semiconductor nanocrystals under conditions in which the polarization interaction of an electron (hole) with a nanocrystal surface plays the dominant role is developed. It is shown that, in the region of interband absorption, the shifts of electron (hole) size-quantization levels in a nanocrystal subjected to an external homogeneous electric field are governed by the quadratic Stark effect. A new electrooptical method is proposed furnishing an opportunity to determine the critical radii of nanocrystals in which bulk excitons can appear.     

Trapped plasma oscillations in unipolar semiconductor structures

Based on the results of a large-signal computer simulation, a trapped plasma mode of oscillation is described in an n+-n-n+ silicon structure. The mechanism is similar to TRAPATT in many ways, but relies upon space-charge injection of majority carriers rather than a depletion region for the necessary initial electric field profile. A necessary design criteria ofN_{d}L < 10^{12}cm^-2is established.     

Barrier studies on porous silk semiconductor dielectric

Barrier integrity of Ta-films deposited using the enhanced coverage by re-sputtering (EnCoRe¹) barrier was investigated on untreated surfaces of blanket porous SiLK^{, 2} semiconductor dielectric (developmental version 7, hereinafter v7). Barrier integrity of a bi-layer EnCoRe Ta(N)/Ta film was studied on single damascene lines using v7 and porous SiLK semiconductor dielectric (developmental version 9, hereinafter v9). On blanket wafers more than 30 nm barrier thickness is necessary to achieve complete pore sealing. Analysis of the sheet resistance showed that when tantalum is deposited, a low resistivity -phase is nucleated on the low-k surface. When deposited onto single damascene structures, EnCoRe Ta(N)/Ta is successful in providing a continuous metallic barrier layer over v7 and v9 semiconductor dielectric lines.     

Transport boundary condition for semiconductor structures

Boundary conditions (BCs) to the Poisson and transport equations for stationary transport processes of non-equilibrium carriers in semiconductor structures are formulated. The applicability of the resulting BCs for several materials (metals, bipolar semiconductors, including ones in the quasineutrality approach, QNA) and their structures are analyzed for both closed and open circuits. As a first step, general BCs for different types of contacts between two materials and between a solid and the vacuum under thermodynamic equilibrium conditions are thoroughly discussed. Later on, BCs are presented for the general case of a contact between a solid (this contact is considered as a “free-surface” in a broad sense) and the vacuum under non-equilibrium conditions. The concept of “free-surface”, and its BCs, can be extended and applied to other interfaces such as semiconductor–insulator that is relevant in semiconductor devices. Finally, the case of a hetero-contact between two conducting media under a current flow is addressed. BCs for closed-circuit conditions are presented and it is shown that BCs for open-circuit can be obtained as a limit of the proposed ones when the electric current tends to zero. In all the considered cases the changes operated in the BCs if the QNA is invoked are carefully studied.     

Controllable growth of semiconductor nanometer structures

Self-assembled quantum dots and wires were obtained in the In_xGa_1-xAs/GaAs and InAs/In_0.52Al_0.48As/InP systems, respectively, using molecular beam epitaxy (MBE). Uniformity in the distribution, density, and spatial ordering of the nanostructures can be controlled to some extent by adjusting and optimizing the MBE growth parameters. In addition, some interesting observation on the InAs wire alignment on InP(001) is discussed.