On the injection current mechanism in light-emitting p-i-n structures based on a-Si1?xCx:H hydrogenated amorphous alloys

Current-voltage (I–V) characteristics of thin-film p-i-n nd pDiDn tructures in which the i layer is based on a-Si_1−x C_x:H hydrogenated amorphous alloys and the p and n layers are composed of doped a-Si:H were studied. To account for the specific features of these I–V characteristics, i.e., the small values of the constant Ain the exponential dependence of the current on the voltage, I ∝ exp(AV), a mechanism of tunneling injection from the n layer directly into the tail of localized states is suggested. The tunneling process has a multistep nature and is, in general terms, similar to the recombination current in heterojunctions. The high density of localized states in the energy gap of a-Si_1−x C_x:H near the band edge (∼10²⁰–10²¹ cm⁻³), as well as the density’s dependence on the composition of this compound, make it possible to obtain a constant A close to the experimental value and to explain the decrease in A, which is observed as the content of carbon in the alloy increases. At high biases, there occurs a transition from monopolar to double injection and from the nonradiative to radiative recombination of nearly free electrons and holes. Structures with x = 0.4–0.6 exhibited a weak electroluminescence in the visible spectral range, with the emission peak being Stokes-shifted by ∼0.25E _g of the i layer. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 39, No. 2, 2005, pp. 276–280. Original Russian Text Copyright ? 2005 by Andreev.     

<Emphasis Type="Italic">C-V</Emphasis> and <Emphasis Type="Italic">I-V</Emphasis> characteristics of ultrathin-oxide MOS structures: Identification and analysis

For an NMOS structure with 3.7-nm-thick oxide, dynamic I-V characteristics are digitally measured by applying an upward and a downward gate-voltage ramp. An averaging procedure is employed to deduce the tunneling (active) current component and the quasi-static C-V characteristic (CVC). Analyzing the depletion segment of the CVC provides reliable values of the semiconductor doping level, the oxide capacitance and thickness, and the sign and density of oxide-fixed charge, as well as estimates of the dopant concentration in the poly-Si region. These data are used to identify the Ψ_s(V _g), V _i(V _g), and I _t(V _i) characteristics, where Ψ_s is the n-Si surface potential, V _i is the voltage drop across the oxide, V _g is the gate voltage, and I _t is the tunneling current; the gate-voltage range explored extends to prebreakdown fields (～13 MV cm^?1). The results are obtained without recourse to fitting parameters and without making any assumptions as to the energy spectrum of electrons tunneling from the n-Si deep-accumulation region through the oxide. It is believed that experimental I _t-V _i and Ψ_s-V _g characteristics will provide a basis for developing a theory of tunneling covering not only the degeneracy and size quantization of the electron gas in the semiconductor but also the nonclassical profile of the potential barrier to electron tunneling associated with the oxide-fixed charge.     

Defect-Related White-Light Emission from ZnO in an n-Mg0.2Zn0.8O/n-ZnO/SiOx Heterostructure on n-Si

An n-Mg_0.2Zn_0.8O/n-ZnO/SiO _x (x < 2) heterostructure has been fabricated on n-Si by sputtering and electron-beam evaporation. The device showed nonrectifying behavior, and emitted strong white light under reverse bias with positive voltages applied to n-Si. The white-light electroluminescence (EL) is believed to result from electron–hole recombination at defect levels of ZnO. The EL mechanism has been tentatively explained in terms of the energy band structure of the device under forward and reverse bias.     

Technological Features of Irradiation of Sip+-n-n+ Diodes with Electrons at Elevated Temperatures

The behavior of the lifetime of nonequilibrium charge carriers τ_p, the reverse current I _R, and the forward-voltage drop U _F in electron-irradiated (E _irr = 6 MeV) commercial p ⁺-n-n ⁺ diodes at irradiation temperatures in the range of T _irr = 20–400°C is studied. Studies have been performed for samples fabricated on a single-crystal Si substrate either doped with phosphorus in the course of growth by the Czochralski method (Cz-n-Si:P) or doped with phosphorus by nuclear transmutations, neutron-transmutation doped Si (NTD n-Si:P). It is shown that, by choosing the temperature conditions of technological irradiation, one can solve the problem of attaining small values of τ_p at a minimal increase in U _F and I _R in fast-response diodes. It is established that, in the case of comparable variations in τ_p in the base region of diodes, the best relation between U _F and I _R is observed at T _irr = 300°C in n-Si:P samples doped by the Czochralski method and at T _irr = 350°C in samples doped by reactions induced by thermal neutrons.     

Influence of deep traps on current transport in Pd-p(n)-CdTe structures

The current-voltage characteristics and photovoltage of Pd-p(n)-CdTe structures and changes in them produced by pulsed hydrogen treatment have been investigated. The current transport in Pd-n-CdTe structures [I∼exp(αV)] is found to be linked with double injection of carriers occurring as a result of their capture at trapping centers that are uniformly distributed over energy. The semiconductor regime of double injection with I∼V ² is important for Pd-p-CdTe structures. A series of deep trapping centers, including those in the interval 0.75–0.83 eV, is responsible for the extended relaxation of the photovoltage and dark current after a hydrogen pulse (H₂). Fiz. Tekh. Poluprovodn. 33, 492–493 (April 1999)     

Effects of the electrical stress on the conduction characteristics of metal gate/MgO/InP stacks

The degradation dynamics and post-breakdown current–voltage (I–V) characteristics of magnesium oxide (MgO) layers grown on n and p-type indium phosphide (InP) substrates subjected to electrical stress were investigated. We show that the current–time (I–t) characteristics during degradation can be described by a power-law model I(t) = I₀t^−α, where I₀ and α are constants. It is reported that the leakage current associated with the soft breakdown (SBD) failure mode follows the typical voltage dependence I = aV^b, where a and b are constants, for both injection polarities but in a wider voltage range compared with the SiO₂/Si system. It is also shown that the hard breakdown (HBD) current is remarkably high, involving large ON–OFF fluctuations that resemble the phenomenon of resistive switching previously observed in a wide variety of metal oxides.     

Differential resistance of Au/GaAs1−x Sbx tunneling contacts in the zero-bias anomaly region. I. Contacts to n-GaAs1−x Sbx

The current-voltage characteristics and the differential resistance R(V)=dV/dI of Au/n-GaAs_1−x Sb_x tunneling contacts were investigated. Schottky barriers were prepared on n-GaAs_1−x Sb_x epitaxial layers, which were specially not doped, in the composition range 0.01<x<0.125. It was shown that the curves R(V) in the electron density range 2×10¹⁸⩽n⩽7×10¹⁸ cm⁻³ and temperature range 4.2⩽T⩽295 K are described well by the tunneling theory employing a self-consistent calculation of the potential in the Schottky barrier region. A square-root dependence of the conductance G(V)=(dV/dI)⁻¹ on the bias voltage V was observed in the zero-bias anomaly region in accordance with the Al’tshuler-Aronov theory of quantum corrections introduced in the density of states at the Fermi level by the characteristic features of the electron-electron interaction in disordered metals. Fiz. Tekh. Poluprovodn. 32, 574–578 (May 1998)     

Investigation of the Mθ/G/1/m system with service regime switchings and threshold blocking of the input flow

The M^θ/G/1/m queueing system with the group arrival of customers, switchings of service regimes, and threshold blocking of the flow of customers is studied. The input flow is blocked if, at the instant of the successive customer service start, the number of customers in the system exceeds specified threshold level h. If, at instant t of the customer service start, number of customers in the system ξ(t) satisfies the condition h_i < x(t) \leqslant h_{i + 1} (i = [`(1,r)] )h_i < \xi (t) \leqslant h_{i + 1} (i = \overline {1,r} ), then the service time for this customer corresponds to distribution function F _i (t). At 1 ≤ ξ(t) ≤ h = h ₁, the service time for a customer is distributed according to law F(t) (basic service time). The Laplace transforms for the distribution of the number of customers in the system on the busy period and for the distribution function of the busy period are found, the mean length of the busy period (including the case m = ∞) is determined and formulas for the ergodic distribution of the number of customers in the system (including the case m = ∞) are obtained. An effective algorithm for calculation of the ergodic distribution is proposed. The recurrence relations of the algorithm are not explicitly dependent on m.     

Nonmonotonic variations in the concentration of the donor-and acceptor-type radiation defects in silicon irradiated with low-intensity fluxes of β particles

Deep-level transient spectroscopy is used to study the dependence of the concentration of the donor-and acceptor-type radiation defects in silicon on the duration of irradiation with low-intensity fluxes of β particles (I ≈ 9 × 10⁵ cm^?2 s^?1). It is found that the concentrations of the defects C _i , C _i -C _s , and/or V-O in n-Si and the defects V-B, C _i -O _i , and/or V ₂-O-C in p-Si vary nonmonotonically.     

Features of the current-voltage characteristics of long semiconductor structures under ultrahigh-level double-injection conditions

The widespread use of low-resistivity materials in modern solid-state electronics calls for an analysis of the current-voltage characteristics of long semiconductor structures under ultrahighlevel double-injection conditions. It is shown that the pure plasma model of semiconductors is not applicable in such an analysis, since the concentration dependence of the carrier mobility μ(n) must be taken into account. The conditions for the appearance of highly superlinear current-voltage characteristics in the region of the initial variation of μ(n) due only to the rate of variation of the mobility of the majority carriers (the λ effect) are analyzed. The λ effect is manifested on the experimental current-voltage characteristics in the form of sharp current jumps and corresponding high values of the differential order of the current-voltage (J-V) characteristic (a=d log J/d log V), which are determined by the variation of the differential order of the concentration dependence of the carrier mobility λ(n)=d log μ/d log n. A calculation shows that the mechanism for the appearance of the λ effect can be determined at injection levels as high as ∼10¹⁷ cm⁻³. Fiz. Tekh. Poluprovodn. 32, 1476–1481 (December 1998)     

Frequency characteristics of diodes with intervalley electron transfer that are based on variband In x ( z )Ga1 ? x ( z )As with various cathode contacts

A two-level model of intervalley electron transfer in a variband semiconductor is used to study the operation of a Gunn diode based on variband In _x(z)Ga_{1 − x(z)}As with n ⁺-n cathodes and n ⁺-n ⁻-n cathodes for different lengths of the active region and different thicknesses of the variband layer. It is demonstrated that the critical frequency of a GaAs-In_0.4Ga_0.6As diode (280–290 GHz) is higher than the critical generation frequencies of GaAs, In_0.4Ga_0.6As, and In_0.2Ga_0.8As diodes. Original Russian Text ? I.P. Storozhenko, 2007, published in Radiotekhnika i Elektronika, 2007, Vol. 52, No. 10, pp. 1253–1259.     

Electrical measurements of voltage stressed Al2O3/GaAs MOSFET

Electrical characteristics of GaAs metal–oxide–semiconductor field effect transistor with atomic layer deposition deposited Al₂O₃ gate dielectric have been investigated. The IV characteristics were studied after various constant voltage stress (CVS) has been applied. A power law dependence of the gate leakage current (I_g) on the gate voltage (V_g) was found to fit the CVS data of the low positive V_g range. The percolation model well explains the degradation of I_g after a high positive V_g stress. A positive threshold voltage (V_th) shift for both +1.5 V and +2 V CVS was observed. Our data indicated that positive mobile charges may be first removed from the Al₂O₃ layer during the initial CVS, while the trapping of electrons by existing traps in the Al₂O₃ layer is responsible for the V_th shift during the subsequent CVS.     

Growth of (InSb)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(Sn<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films on GaAs substrates by liquid-phase epitaxy

The possibility of growing single-crystal substitutional (InSb)_{1 − x} (Sn₂) _x alloy (0 ≤ x ≤ 0.05) on the GaAs substrate by liquid-phase epitaxy from the In solution melt is established. The X-ray diffraction patterns and spectral and current-voltage characteristics of obtained n-GaAs-p-(InSb)_{1 − x} (Sn₂) _x heterostructures are studied at different temperatures. The lattice parameters of the (InSb)_{1 − x} (Sn₂) _x alloy are determined. It is found that the forward portion of the current-voltage characteristic of such structures at low voltages (up to 0.7 V) is described by the exponential dependence I = I ₀exp(qV/ckT), and at high voltages (V > 0.9 V), there is a portion of sublinear increase in the current with the voltage V ≈ V ₀exp(Jad). The experimental results are interpreted based on the injection depletion theory. It is shown that the product of mobility of majority carriers by the concentration of deep-level impurities increases as the temperature increases.     

1/f noise in large-area Hg<Subscript>1−x</Subscript>Cd<Subscript>x</Subscript>Te photodiodes

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg_1−xCd_xTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10⁻¹⁵A/Hz^1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth i_n(f = 1 Hz, V_d = −60 mV, and Δf = 1 Hz) to dark current I_d(V_d = −60 mV) was α_SW-d = i_n/I_d ∼ 1 × 10⁻³. The SWIR detectors measured at 0 mV under illuminated conditions had median α_SW-P = i_n/I_ph ∼ 7 × 10⁻⁶. For mid-wave infrared (MWIR) detectors, α_MW-d = i_n/I_d ∼ 2 × 10⁻⁴, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in α_MW-P = i_n/I_ph = 4.16 ± 1.69 × 10⁻⁶. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, α_MW-P, in the mid 10⁻⁶ range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, α_LW-d = i_n/I_d ∼ 6 × 10⁻⁶, for the best performers. The majority of the LWIR detectors exhibited α_LW-d on the order of 2 × 10⁻⁵. The photo-induced 1/f noise had α_LW-P = i_n/I_ph ∼ 5 × 10⁻⁶. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.     

Spreading resistance and compensation of charge carriers in ferromagnetic silicon implanted with manganese

Profiles of impurity distribution and spreading resistance have been studied in the layers of ferromagnetic silicon obtained by implantation of Mn (or Co). Standard wafers of n- and p-Si with a high or low electrical conductivity were implanted with Mn ions with the dose (1−5) × 10¹⁶ cm⁻². It is found that, as a result of postimplantation annealing in vacuum for 5 min at 850°C, Mn manifests itself as an amphoteric impurity and compensates acceptors in high-resistivity p-Si and donors in low-resistivity n-Si. It is shown that only an insignificant fraction of Mn ions (1–2%) is electrically active and is involved in compensation. The magnitude of compensation is used to determine energies of the levels E _c − 0.12 eV for n-Si and E _v + 0.32 eV for p-Si; these levels are attributed to Mn ions at interstitial sites in the silicon crystal lattice, i.e., (Mn _i )^−/0 and (Mn _i )^+/++, respectively.     

Specific features of intervalley scattering of charge carriers in <Emphasis Type="Italic">n</Emphasis>-Si at high temperatures

In n-Si, intervalley scattering of electrons can be of two types, f scattering and g scattering. With the purpose of establishing the contributions of f- and g-type transitions to intervalley scattering, the piezoresistance of n-Si crystals is studied in the temperature range T = 295–363 K. The initial concentration of charge carriers in the n-Si samples is 1.1 × 10¹⁴ cm⁻³, and the resistivity at 300 K is ρ = 30 Ω cm. As the temperature is increased, the region of leveling-off of the piezoresistance shifts to lower voltages. The characteristic feature of the dependence ρ = ρ(T) plotted in the double logarithmic coordinates (logρ = f(logT)) is the transition from the slope 1.68 to the slope 1.83 at T > 330 K. This is attributed to the substantial contribution of g transitions to intervalley scattering in the high-temperature region. For verification of the interpretation of the dependence ρ = ρ(T), the dependence is calculated on the basis of the theory of anisotropic scattering with consideration for intervalley transitions.     

Fabrication and Electrical Characterization of Heterojunction Mn-Doped GaN Nanowire Diodes on <Emphasis Type="Italic">n</Emphasis>-Si Substrates (GaN:Mn NW/<Emphasis Type="Italic">n</Emphasis>-Si)

We demonstrated that manganese (Mn)-doped GaN nanowires (NWs) exhibit p-type characteristics using current–voltage (I–V) characteristics in both heterojunction p–n structures (GaN:Mn NWs/n-Si substrate) and p–p structures (GaN:Mn NWs/p-Si). The heterojunction p–n diodes were formed by the coupling of the Mn-doped GaN NWs with an n-Si substrate by means of an alternating current (AC) dielectrophoresis-assisted assembly deposition technique. The GaN:Mn NWs/n-Si diode showed a clear current-rectifying behavior with a forward voltage drop of 2.4 V to 2.8 V, an ideality factor of 30 to 37, and a parasitic resistance in the range of 93 kΩ to 130 kΩ. On the other hand, we observed that other heterojunction structures (GaN:Mn NWs/p-Si) showed no rectifying behaviors as seen in p–p junction structures.     

Electrical and photoelectric properties of anisotype n-TiN/p-Si heterojunctions

Photosensitive n-TiN/p-Si heterojunctions are fabricated by the reactive magnetron sputtering of a thin titanium-nitride film with n-type conductivity onto polished polycrystalline p-Si wafers. The I–V characteristics of the heterostructures are measured at different temperatures. The temperature dependences of the potential-barrier height and series resistance of the n-TiN/p-Si heterojunction are studied. The dominant mechanisms of current transport through the heterojunction in the cases of forward and reverse bias are established. The heterostructures generate the open-circuit voltage V _oc = 0.4 V and the short-circuit current I _sc = 1.36 mA/cm² under illumination with a power density of 80 mW/cm².