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.     

Isotype surface-barrier n-TiN/n-Si heterostructure

n-TiN/n-Si heterostructures are prepared by reactive magnetron sputtering. The current-voltage characteristics of the heterostructures are measured at different temperatures. The temperature dependences of the potential-barrier height and the series resistance of the heterojunction are analyzed. The energy-band diagram for the heterojunctions under study is constructed. The concentration of heterojunction surface states is estimated to be 2.67 × 10¹³ cm^?2. It is established that the dominant mechanisms of current transport through forward- and reverse-biased n-TiN/n-Si heterojunctions are described well within the tunnel and emission models.     

Electrical Characteristics of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Si Heterojunction Diodes Grown by Pulsed Laser Deposition at Different Oxygen Pressures

Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at different pressures. These heterojunctions were found to be rectifying with a maximum forward-to-reverse current ratio of about 1,000 in the applied voltage range of −5 V to +5 V. The turn-on voltage of the heterojunctions was found to depend on the ambient oxygen pressure during the growth of the ZnO film. The current density–voltage characteristics and the variation of the series resistance of the n-ZnO/p-Si heterojunctions were found to be in line with the Anderson model and Burstein-Moss (BM) shift.     

Electrical and photoelectric properties of <Emphasis Type="Italic">n</Emphasis>-TiN/<Emphasis Type="Italic">p</Emphasis>-Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> heterostructures

n-TiN/p-Hg₃In₂Te₆ heterostructures are fabricated by depositing a thin n-type titanium nitride (TiN) film onto prepared p-type Hg₃In₂Te₆ plates using reactive magnetron sputtering. Their electrical and photoelectric properties are studied. Dominant charge-transport mechanisms under forward bias are analyzed within tunneling-recombination and tunneling models. The fabricated n-TiN/p-Hg₃In₂Te₆ structures have the following photoelectric parameters at an illumination intensity of 80 mW/cm²: the open-circuit voltage is V_OC = 0.52 V, the short-circuit current is I_SC = 0.265 mA/cm², and the fill factor is FF = 0.39.     

Specific features of the recombination loss of the photocurrent in n-TiN/p-Si anisotype heterojunctions

Photosensitive n-TiN/p-Si heterostructures are fabricated by reactive magnetron sputtering. The heterostructures generate an open-circuit voltage of V _oc = 0.4 V and a short-circuit current of I _sc = 1.36 mA/cm² under illumination at 80 mW/cm². An analysis of the light current-voltage characteristic and quantum-yield spectrum demonstrate that the poor photoelectric parameters are due to recombination in the base region of the heterojunction and to the formation of a high-resistivity SiO₂ layer on the surface of polycrystalline silicon, which fails to provide high-quality passivation of surface states.     

Photoelectric properties of isotype and anisotype Si/GaN:O heterojunctions

Results of a comprehensive study of electrical and photoelectric properties of isotype (p-Si/p-GaN:O) and anisotype n-Si/p-GaN:O) heterojunctions are reported. The structures were fabricated by chemical vapor deposition of thin films of GaN:O solid solutions on silicon substrates by pyrolytic decomposition of gallium monoammine chloride in the presence of water vapor. Total and spectral photosensitivity and photoresponse kinetics in the current mode under forward and reverse biases, current-voltage characteristics, and saturation open-circuit photovoltage were studied. It was found that in both kinds of heterojunctions the charge distribution near the contacts is mainly governed by carrier capture into interface states (with density estimated to be ～10¹⁴–10¹⁵ cm^?2) with the formation of depletion layers on both sides of the interface. Photosensitivity mechanisms are analyzed for anisotype and isotype heterojunctions. It is shown that the differential nature of the photoresponse kinetics is related to the recharging of interface states, and the strong rise in the photoresponse signal of a biased anisotype heterojunction is attributed to the phototransistor effect. The proposed energy band models of the heterojunctions consistently describe the observed effects.     

Low resistivep-type ZnSe: A key for an efficient blue electroluminescent device

Highly conductivep-type ZnSe layers have been grown on GaAs substrates by vapor phase epitaxy in an open system. Iodine and hydrogen were used as transport agents. The ZnSe layers exhibited a conductivity up to 50 (Ωcm)⁻¹ and a carrier concentration of 4 × 10¹⁸ cm⁻³ together with a Hall mobility of 100 cm²/Vs. These values are the highest ones reported so far. Low-temperature photoluminescent spectra indicated new bound excitons. Electroluminescent metal/p-ZnSe/n-GaAs heterojunctions exhibited blue emission at 2.68 eV dominating the spectra.     

Growth and characterization of undoped and N-type (Te) doped MOVPE grown gallium antimonide

The growth of GaSb by MOVPE and itsn-type doping using a dimethyltellurium dopant source are investigated. The results of growth rate, morphology and Te incorporation as a function of growth parameters are given. Increasing growth temperature and V/III reactant ratio were found to reduce the Te incorporation. The lowest Hall carrier concentrations obtained at room-temperature, onp-type andn-type MOVPE GaSb are respectively:p _H= 2.2 × 10¹⁶cm⁻³ with a Hall mobility ofμ _H= 860 cm²/V.s andn _H= 8.5 × 10¹⁵cm⁻³ withμ _H= 3860 cm²/V.s. Furthermore, Hall mobilities as high as 5000 cm²/V.s were measured onn-type GaSb samples.     

Hybrid Inorganic–Organic Heterojunction Solar Cell

In this study, solar cells were fabricated by spin-coating polyaniline (PANI) base (EB) over an n-type Si substrate. The final heterojunction’s device structure was Al/n-type Si/EB/Au. The electrical properties of the resultant device were investigated by measuring the current density–voltage (J–V), capacitance–voltage (C–V), and impedance characteristics in the dark and under illumination. N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and tetrahydrofuran (THF) were used as solvents for EB. The effects of these solvents on the photovoltaic cell parameters were investigated, and the open-circuit voltage (V _oc), short-circuit current density (J _sc), fill factor (FF), and energy conversion efficiency (η) were determined. It was found that heterojunctions fabricated using EB dissolved in NMP, DMF, and THF produced J _sc of 10 mA/cm², 5.123 mA/cm², and 2.78 mA/cm², respectively. Rollover and crossover phenomena in the J–V curves under illumination were explained based on the back-contact barrier and surface recombination of electrons at the back contact. The linearity of Mott–Schottky plots indicated the formation of a heterojunction between EB and n-type Si, and the slope of 1/C ² versus voltage changed under illumination. The high values of shunt resistance were decreased under illumination, indicating that the efficiency of this type of heterojunction solar cell was limited by shunt resistance and the narrow absorption range of the solar spectrum by EB.     

Ultra-violet photo-response characteristics of p-Si/i-SiO2/n-ZnO heterojunctions based on hydrothermal ZnO nanorods

Hydrothermal zinc oxide (ZnO) nanorod (NR)-based p-Si/n-ZnO and p-Si/i-SiO₂/n-ZnO heterojunctions were fabricated, and the effects of interfacial native SiO₂ (~4 nm) on the I-V characteristics of heterojunctions under dark and ultra-violet illumination conditions were investigated. First, the structural and optical properties of ZnO seed crystals grown by sol-gel method and hydrothermal ZnO NRs on two different substrates of p-Si and p-Si/i-SiO₂ were examined, and more improved optical and crystalline quality was obtained as revealed by photoluminescence and X-ray diffraction. The p-i-n heterojunctions showed ~3 times greater forward-bias currents and enhanced rectifying property than those of p-n junctions, which is attributed to the role of native SiO₂ in carrier confinement by promoting the electron-hole recombination current through the deep level states of ZnO crystal. The measured ratios of photocurrent to dark current of the p-i-n structure were also greater under reverse bias (92–260) and forward bias (2.3–7.1) conditions than those (28–225 for reverse bias, 1.6–6.8 for forward bias) of p-n structure, and the improved photosensitivity of the p-i-n structure under reverse bias is due to lower density of recombination centers in the ZnO NR crystals. Fabricated ZnO NR heterojunction showed repeatable and fast photo-response transients under forward bias condition of which response and recovery times were 7.2 and 3.5 s for p-i-n and 4.3 and 1.7 s for p-n structures, respectively.     

Charge transport mechanisms in anisotype n-TiO2/p-Si heterostructures

Anisotype n-TiO₂/p-Si heterojunctions are fabricated by the deposition of a TiO₂ film on a polished poly-Si substrate using magnetron sputtering. The electrical properties of the heterojunctions are investigated and the dominant charge transport mechanisms are established; these are multi-step tunneling recombination via surface states at the metallurgical TiO₂/Si interface at low forward biases V and tunneling at V > 0.6 V. The reverse current through the heterojunctions under study is analyzed within the tunneling mechanism.     

Electrical Properties of Organic–Inorganic Semiconductor Device Based on Rhodamine-101

Rhodamine-101 (Rh101) thin films on n-type Si substrates have been formed by means of evaporation, thus Sn/Rh101/n-Si heterojunctions have been fabricated. The Sn/Rh101/n-Si devices are rectifying. The optical energy gaps have been determined from the absorption spectra in the wavelength range of 400 nm to 700 nm. Rh101 has been characterized by direct optical absorption with an optical edge at 2.05 ± 0.05 eV and by indirect optical absorption with␣an optical edge at 1.80 ± 0.05 eV. It was demonstrated that trap-charge-limited current is the dominant transport mechanism at large forward bias. A␣mobility value of μ = 7.31 × 10⁻⁶ cm² V⁻¹ s⁻¹ for Rh101 has been obtained from the forward-bias current–voltage characteristics.     

Simultaneous Formation of Ni/Al Ohmic Contacts to Both n- and p-Type 4H-SiC

The fabrication procedure for silicon carbide power metal oxide semiconductor field-effect transistors can be improved through simultaneous formation (i.e., using the same contact materials and a one-step annealing process) of ohmic contacts on both the n-source and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n- and p-type SiC after annealing at 1000°C for 5 min in an ultrahigh vacuum. Ohmic contacts to n-type SiC were found when the Al-layer thickness was less than about 6 nm, while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with an Al-layer thickness in the range of 5 nm to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with a specific contact resistance of 1.8 × 10⁻⁴ Ω cm² and 1.2 × 10⁻² Ω cm² for n- and p-type SiC, respectively. An about 100-nm-thick contact layer was uniformly formed on the SiC substrate, and polycrystalline δ-Ni₂Si(Al) grains were formed at the contact/SiC interface. In the samples that exhibited ohmic behavior to both n- and p-type SiC, the distribution of the Al/Ni ratios in the δ-Ni₂Si(Al) grains was larger than that observed for any of the samples that showed ohmic behavior to either n- or p-type SiC. Furthermore, the grain size of the δ-Ni₂Si(Al) grains in the samples showing ohmic behavior to both n- and p-type SiC was smaller than the grains in any of the samples that showed ohmic behavior to either n- or p-type SiC. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the ohmic contacts to both n- and p-type SiC. Grains with a low Al concentration correspond to ohmic contacts to n-type SiC, while grains with a high Al concentration correspond to ohmic contacts to p-type SiC.     

Electrical and gas sensing properties of <Emphasis Type="Italic">por</Emphasis>-Si/SnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposite layers

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnO _x , fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnO _x nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnO _x nanocomposites to NO₂ is determined. A mechanism for the effect of the adsorption of NO₂ molecules on the current-voltage characteristics of the por-Si(p)/SnO _x (n) heterojunctions is suggested.     

Gamma-induced metastable states of doped, amorphous, hydrated silicon

The temperature dependence of the electrical conductivity of B-and P-doped a-Si:H films before and after irradiation with γ rays from a ⁶⁰Co source has been investigated. The irradiation dose was 10¹⁷–10¹⁸ photons/cm². The behavior of the n-type films was observed to be substantially different from that of the p-type films. The electrical conductivity of the p-type films increases slightly (by a factor of 2–3) and that of the n-type films decreased sharply (by 2–3 orders of magnitude). The observed difference is explained by the different character of the γ-irradiation-induced charge redistribution on the broken silicon bonds D⁺ and D⁻. Comparing the results with the published data shows that the γ rays induce metastable states of a-Si:H which are due to the motion of bound hydrogen. Fiz. Tekh. Poluprovodn. 32, 245–248 (February 1998)     

Properties of Mn-doped p-type InxGa1-xAsyP1-y grown by liquid-phase epitaxy

Epitaxial layers of p-type In_xGa_1-xAs_yP_1-y doped with Mn were grown by liquid-phase epitaxy on (111)-B oriented InP substrates at a growth temperature of 635°C. The doping characteristics and electrical and luminescent properties were studied and compared with those in Zn-doped epilayers. The distribution coefficient of Mn was about 0.1–0.3. The p-type epilayers with hole concentration of up to 3 × 10¹⁸ cm^?3 could be easily obtained by Mn doping. The activation energy of the Mn acceptor was about 40 meV. Mn doping yielded a broad photoluminescent emission spectrum which probably arises from d-shell interaction of the Mn as well as strong phonon coupling. From electron beam-induced current measurements in p-n heterojunctions utilizing Mn, a value of L_n = 2 μm was obtained for the minority carrier diffusion length of electrons in the p-type region.     

Carrier Transport Mechanism and Band Offsets at the Interface of ZnS/<Emphasis Type="Italic">n</Emphasis>-Si (111) Heterojunctions Fabricated by Vacuum Thermal Evaporation

The electrical properties and band offset of ZnS/n-Si(111) heterojunctions with and without annealing were analyzed. The result showed that the rectifying characteristics of ZnS/n-Si(111) heterojunctions became better and the leakage current increased after annealing. This phenomenon is mostly due to the volatilization of S atoms of ZnS films and leads to defect levels appearing at the interface of the ZnS/n-Si(111) hetrojunctions. The valence band offset (ΔE _V) of the ZnS/n-Si(111) heterojunctions can be calculated to be ?0.7 ± 0.15 eV by means of photoelectron spectroscopy, indicating that the band offsets of ZnS/n-Si(111) heterojunctions show a type-II band alignment.     

Degradation of MOS tunnel structures at high current density

The stability of tunneling-thin (2–3 nm) SiO₂ films during prolonged flow of high-density currents (10²–10³ A/cm²) was investigated. A sharp increase in the charge which a tunneling MOS structure is capable of transmitting without degradation on switching from Fowler-Nordheim injection to direct tunneling (10³ C/cm² and 10⁷ C/cm², respectively) was observed. The degradation of SiO₂ films was investigated using Al/SiO₂/n-Si/p ⁺-Si thyristor structures with a positive bias on the semiconductor, i.e., with reverse bias of the MOS structure. The use of these devices accounted for the uniformity of the current distribution over the area and made it possible to monitor the state of the insulator layer by measuring the device gain in the phototransistor mode. Fiz. Tekh. Poluprovodn. 32, 743–747 (June 1998)     

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.     

Mechanisms of charge transport in anisotype <Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

Surface-barrier anisotype n-TiO₂/p-CdTe heterojunctions are fabricated by depositing thin titanium-dioxide films on a freshly cleaved surface of single-crystalline cadmium-telluride wafers by reactive magnetron sputtering. It is established that the electric current through the heterojunctions under investigation is formed by generation-recombination processes in the space-charge region via a deep energy level and tunneling through the potential barrier. The depth and nature of the impurity centers involved in the charge transport are determined.