Depletion region

About: Depletion region is a research topic. Over the lifetime, 9393 publications have been published within this topic receiving 145633 citations.

E-Mode High Electron Mobility Transistors And Methods Of Manufacturing The Same

Abstract: An Enhancement-mode (E-mode) high electron mobility transistor (HEMT) includes a channel layer with a 2-Dimensional Electron Gas (2DEG), a barrier layer inducing the 2DEG in the channel layer, source and drain electrodes on the barrier layer, a depletion layer on the barrier layer between the source and drain electrodes, and a gate electrode on the depletion layer. The barrier layer is recessed below the gate electrode and the depletion layer covers a surface of the recess and extends onto the barrier layer around the recess.

Silicon-on-Insulator Based Thin-Film Resistor for Chemical and Biological Sensor Applications

Abstract: Efficient detection of specific or nonspecific interactions at solid ± liquid interfaces is becoming increasingly important for a wide variety of applications and technologies, which range from industrial and biomedical applications to basic research. 2] The most prominent example of applications in basic research is the label-free detection of biomolecular interactions. There is growing need for new detection schemes, as the common fluorescent labeling techniques are limiting the applicability of DNA or protein arrays. Increasingly sophisticated techniques are being developed to provide versatile techniques for labelfree detection methods. 5] The main requirement for new technologies is the highly sensitive and specific detection of molecules. At the same time, for the applicability of the technique towards screening of biomolecular interactions, the potential of simultaneous parallel detection is mandatory. Several different approaches have been developed to address these requirements. For the electrical detection of molecular interactions, physical principles of field-effect transistors are used in most cases: Variations of the surface potential induce changes in the charge carrier concentration and thus in the conductivity of the semiconductor. The most extensively studied technique to date is the technology of ion-sensitive field-effect transistors (ISFETs), which have been shown to be versatile tools for detecting chemical and enzymatic reactions. The direct electrical detection of cell signaling was realized with recently developed semiconductor chips. 8] The capacitive detection of inversion layers in silicon structures has successfully been used to monitor the hybridization of DNA molecules. A similar approach with a biofunctionalized, porous silicon electrolyte ± insulator ± semiconductor (EIS) structure as a sensing device was used to detect biomolecules, such as penicillin, with a sensitivity down to 10 nM. Here, we present a device based on silicon-on-insulator (SOI) substrates that enables the detection of changes of electrolyte concentrations and of small numbers of charged biomolecules. In the SOI substrates the conducting layer is limited to a thin surface layer, covered by a thin native oxide layer. Hence, the conductivity of this thin conductive layer is strongly dependent on variations of the surface potential and the distribution of the surface states, which results in variations of the space charge region. We utilized a four-point resistance measurement in a hallbar geometry to determine the conductivity of the sensing layer. A variation of the salt concentration of the electrolyte could be detected over five magnitudes and an excellent agreement with the Grahame equation was found. The unspecific adsorption of poly-L-lysine was detectable at concentrations of 1 nM (80 ngmL ). The measurements showed that variations of surface charges of 0.01 e per nm, or one electronic charge per 100 nm, could be detected by the device. For the experiments, commercially available SOI wafers (ELTRAN, Canon) were used. The silicon layer in these wafers was 30 nm thick and was slightly doped with boron (10 cm ). To control the concentration of charge carriers in this layer, a voltage was applied to the backgate of the substrate. For some experiments, this upper silicon layer was overgrown by molecular beam epitaxy (MBE) with a 50 nm thick, single crystalline layer of doped silicon. The p-doping concentration of boron was 10 cm 3 or 10 cm . A sketch of the SOI device is given in Figure 1. In the subsequent steps, the silicon layer was patterned

Semiconductor schottky device with pn regions

Abstract: A semiconductor device has a first diode having a pn junction and a second diode having a combination of a Schottky barrier and a pn junction in a current-passing direction provided side by side in a direction perpendicular to the current-passing direction. When a forward current with a current density JF is passed into the second diodes, the relation ##EQU1## is established in a forward voltage VF range of 0.1 (V) to 0.3 (V), where k represents the Boltzmann constant, T represents the absolute temperature, and q represents the quantity of electron charges. The first diode is constituted by a first semiconductor region of one conductive type and a second semiconductor region of the other conductive type provided so as to be adjacent to the first semiconductor region to form a pn junction, so as to be in ohmic contact with one main electrode, and so as to have an impurity concentration higher than that of the first semiconductor region, and the second diode is constituted by the first semiconductor region of the one conductive type and a third semiconductor region of the other conductive type provided so as to be adjacent to the first semiconductor region to form a pn junction, so as to be in contact through a Schottky barrier with the one main electrode, and so as to have an impurity concentration higher than the first semiconductor region.

On the response behavior of fast photoconductive optical planar and coaxial semiconductor detectors

Abstract: Fast optical detectors use photoconductive effects in semiconducting channels or thin films. The behavior of those planar and coaxial detectors is reviewed. It is shown that p-type and n-type materials show different behavior in respect to bandwidth and gain. The strong influence of the contacts is clarified and the surface recombination is taken into account. The bandwidth of those detectors is evaluated and the gain and gain bandwidth product are given in terms of the geometry and material data. Furthermore, the influence of deep levels and of a depletion layer along the surface is considered, which considerably affect the static characteristics as well as the pulse response. Regarding these effects, the different behavior of GaAs- and Ga 0.47 In 0.53 As-conductive photodetectors is demonstrated.

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

Abstract: The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance–capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t 10–90 = 20 ps (at intermediate gains M < 500) and t 10–90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gain–bandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain–bandwidth product, GBW = 19 THz. The impulse response was modeled using a one-dimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v e = 2.3 × 107 cm/s and v h = 1.0 × 107 cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x j = 4 μm and x j = 2 μm, respectively, for a gain of M = 100.