Depletion region

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

Controlled p doping of the hole-transport molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine with tetrafluorotetracyanoquinodimethane

Abstract: We investigate p-type doping of the hole-transport organic molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) with tetrafluorotetracyanoquinodimethane (F4-TCNQ) using direct and inverse photoemission spectroscopy, contact potential difference measurements, and in situ current–voltage (I–V) measurements. The close match between the ionization energy of α-NPD and the electron affinity of F4-TCNQ leads to an efficient charge transfer between highest occupied molecular orbital of the host and lowest occupied molecular orbital of the dopant. The Fermi level moves down towards the valence states by 0.62 eV in the 0.5% doped film with respect to the undoped film, and a narrow space charge layer (∼60 A) forms at the interface with Au. Hole injection in the doped devices increases by several orders of magnitude due to tunneling through the depletion region. The large relaxation energy of the ionized α-NPD molecule limits the movement of the Fermi level and, ultimately, the hol...

Dynamics of photogenerated holes in undoped BiVO4 photoanodes for solar water oxidation

Abstract: The dynamics of photogenerated holes in undoped BiVO4 photoanodes for water splitting were studied using transient absorption spectroscopy, correlated with photoelectrochemical and transient photocurrent data. Transient absorption signals of photogenerated holes were identified using electron/hole scavengers and applied electrical bias in a complete photoelectrochemical cell. The yield of long-lived (0.1–1 s) photogenerated holes is observed to correlate as a function of applied electrical bias with the width of the space charge layer, as determined by electrochemical impedance spectroscopy. The transient absorption decay time constant of these long-lived holes is also observed to be dependent upon the applied bias, assigned to kinetic competition between water oxidation and recombination of these surface accumulated holes with bulk electrons across the space charge layer. The time constant for this slow recombination measured with transient absorption spectroscopy is shown to match the time constant of back electron transfer from the external circuit determined from chopped light transient photocurrent measurements, thus providing strong evidence for these assignments. The yield of water oxidation determined from these measurements, including consideration of both the yield of long-lived holes, and the fraction of these holes which are lost due to back electron/hole recombination, is observed to be in good agreement with the photocurrent density measured for BiVO4 photoanodes as a function of bias under continuous irradiation. Overall these results indicate two distinct recombination processes which limit photocurrent generation in BiVO4 photoanodes: firstly rapid (≤microseconds) electron/hole recombination, and secondly recombination of surface-accumulated holes with bulk BiVO4 electrons. This second ‘back electron transfer’ recombination occurs on the milliseconds–seconds timescale, and is only avoided at strong anodic biases where the potential drop across the space charge layer provides a sufficiently large energetic barrier to prevent this recombination process.

On Mott-Schottky analysis interpretation of capacitance measurements in organometal perovskite solar cells

Abstract: Capacitance response of perovskite-based solar cells (PSCs) can be exploited to infer underlying physical mechanisms, both in the materials bulk and at outer interfaces. Particularly interesting is applying the depletion layer capacitance theory to PSCs, following common procedures used with inorganic and organic photovoltaic devices. Voltage-modulation of the depletion layer width allows extracting relevant parameters as the absorber defect density and built-in potential by means of the Mott-Schottky (MS) analysis. However, the uncritical use of the MS technique may be misleading and yields incorrect outcomes as a consequence of masking effects that accumulation capacitances, commonly observed in PSCs, produce on the measured capacitance value. Rules are provided here to select the measuring frequency that allows extracting depletion layer capacitance, and the voltage range in which it dominates, avoiding accumulation capacitive parasitic contributions. It is noted that the distinction of the depletion c...

Emission probability of hot electrons from silicon into silicon dioxide

Abstract: An experimental method is described for directly measuring the probability of electron emission from the silicon substrate into the SiO2 layer after the electron has fallen through a certain potential drop in traversing the depletion layer and reached the Si‐SiO2 interface. The method is based on optically induced hot‐electron injection in polysilicon‐SiO2‐silicon field‐effect‐transistor structures of reentrant geometry. The emission probability was studied as a function of substrate doping profile, substrate voltage, gate voltage, and lattice temperature. It was found that the hot electrons could be emitted by tunneling as well as by surmounting the Schottky‐lowered barrier. Over‐the‐barrier emission dominates at large substrate voltages, where the emission probability is high, and tunnel emission becomes appreciable and may even dominate at small substrate voltages where the emission probability is low. A simple model was developed based on the assumption that only those hot electrons lucky enough to escape collision with optical phonons were emitted. Using this model, we found that the expression P=A exp(−d/λ) described very well the dependence of the emission probability on doping profile, substrate voltage, and gate voltage. Here A=2.9 is a constant, λ is the optical‐phonon‐electron collision mean free path, d is the distance from the Si‐SiO2 interface where the potential energy is equal to the ’’corrected’’ barrier of (3.1 eV−βEOX1/2 −αEOX2/3ox), βEOX1/2 is the Schottky lowering of the barrier, and αEOX2/3 is a ’’barrier‐lowering’’ term introduced to account for the probability of tunneling. The temperature dependence of the collision mean free path was found to follow the theoretical relationship λ=λo tanh(ER/2kbT), with λo=108 A and ER=0.63 eV. This model is useful for evaluating potential hot‐electron‐related instability problems in IGFET and similar structures.

InP/InGaAs uni-travelling-carrier photodiode with 310 GHz bandwidth

Abstract: The authors have fabricated an InP-InGaAs uni-travelling-carrier photodiode that exhibits a 3 dB bandwidth of 310 GHz and a pulse width (FWHM) of 0.97ps. Both of which are record values for photodetectors operating at a wavelength of 1.55 /spl mu/m. The average electron velocity in the depletion region is estimated to be 3.0/spl times/10/sup 7/ cm/s.