Deep level defects in gamma-ray irradiated ge doped with pb or sn

Abstract

Deep level transient spectroscopy has been used to investigate the electrical properties of deep defect states in γ-ray irradiated Ge doped with the isoelectronic elements Pb or Sn. Three deep levels are observed in the irradiated Pb-doped Ge (E_v +0.28 eV, E_c ?0.33 eV, E_c ?0.39 eV) and two deep levels observed in the Sn-doped Ge (E_v + 0.19 eV, E_c ?0.15 eV). For the same γ-ray irradiation doses, Ge crystals grown from graphite crucibles and doped with Pb or Sn shows about two-thirds the total density of deep level defects observed in undoped Ge grown from synthetic quartz crucibles. All of the defect states observed were removed by a 1 hour, 250°C thermal anneal, and all but the E_c ?0.39 eV state in the Pb-doped material were neutralized by exposure to a low pressure atomic hydrogen plasma.     

Effect of ambient temperature on electrical properties of nanostructure n-ZnO/p-Si heterojunction diode

The nanostructure n-ZnO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and morphological properties of the nanostructure ZnO film have been investigated. The X-ray diffraction spectra indicated that the films are of polycrystalline nature. The scanning electron microscopy images indicate that the surface morphology of ZnO film is almost homogeneous and the ZnO film is consisted of the circular formed with coming together of the nanoparticles. The electrical characterization of nanostructure n-ZnO/p-Si heterojunction diode has been investigated by current–voltage characteristics. The ideality factor (n) of the diode was found for different ambient temperatures and the obtained 6.40 value for 296 K is higher than unity due to the interface states between the two semiconductor materials and series resistance. The values of n increased with decreasing ambient temperature. The reverse current of the diode increased with illumination intensity of 100 mW cm⁻² and the diode gave a maximum open circuit voltage V_oc of 0.19 V and short-circuits current I_sc of 8.03 × 10⁻⁸ A.     

Anisotropy of photoconductivity and nonlinear effects in GaSe monocrystals at high optical excitation

In this work, the photoelectric properties of gallium selenide (GaSe) monocrystals in the edge absorption region, with various configurations of current contacts, at low and high optical excitation levels are investigated. The photoconductivity spectrum behavior is determined by localized electronic and excitonic states along c-axis. It is shown that the localization of electronic and excitonic states in one-dimensional fluctuation potential along c-axis results to an anisotropy in photoconductivity spectrum at various current contacts configurations. At E⊥c the photoconductivity is observed in the hν < E_g and hν > E_g regions. In the case of hv < E_g, the maximum photoconductivity, in the impurity and exciton absorption region are observed at 1.975 eV and 2.102 eV, respectively. With rising of excitation energy level, suppression of photoconductivity in the exciton absorption region and increases in impurity absorption region is observed. At E||c contact configuration, the considerable photoconductivity is observed only in the impurity absorption region, which also increases with rising of excitation level. It is supposed that, suppression of photoconductivity in the exciton absorption region at high excitation levels is connected with exciton-exciton interaction, which results to a nonlinear light absorption. The results are compared with the absorption and photoluminescence measurements.     

Annealing mechanisms of self-interstitial related defect E1=Ec−0.39 eV in irradiated silicon

DLTS and thermally stimulated capacitance (TSCap) studies of α-particle irradiated p-Si were undertaken to obtain additional information about the self-interstitial related defect E1=E_c−0.39 eV. The E1 defect can be retained frozen up to room temperature without any minority carrier injection, but under injection conditions at 77–300 K the E1 becomes mobile. As a result of annealing of the E1 defect, the carbon interstitial concentration grows. The E1 defect production rate under reverse bias as well as thermal annealing behavior depends strongly on the temperature and impurity concentration. Numerical estimates of the E1 migration via a Bourgoin–Corbett mechanism are in good agreement with the experimental data obtained.     

Valence-band offset of p-NiO/n-ZnO heterojunction measured by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to measure the valence-band offset (VBO) of the NiO/ZnO heterojunction grown on quartz substrate by radio frequency (RF) magnetron sputtering. Core levels of Ni 2p and Zn 2p were used to align the VBO of p-NiO/n-ZnO heterojunction. The valence-band offset (ΔEV) is determined to be 1.47 eV. According to the band gap of 3.7 eV for NiO and 3.37 eV for ZnO, the conduction-band offset (ΔEC) in the structure was calculated to be 1.8 eV, and it has a type-II band alignment.     

n-ZnO/LaAlO3/p-Si heterojunction for visible-blind UV detection

A visible-blind UV photodetector (PD) using a double heterojunction of n-ZnO/LaAlO3 (LAO)/p-Si was demonstrated. Inserted LAO layers exhibit electrical insulating properties and serve as blocking layers for photoexcited electrons from p-Si to n-ZnO, leading to an enhanced rectification ratio and a visible-blind UV detectivity of the n-ZnO/LAO/p-Si PDs due to the high potential barrier between LAO and p-Si layers (~2.0 eV). These results support the use of n-ZnO/LAO/p-Si PDs in the visible-blind UV PDs in a visible-light environment.     

同质硅分子束外延层的界面缺陷的研究

对同质硅分子束外延层的界面缺陷进行了测试与分析．对存在高浓度施主型界面缺陷的Ｐ型材料，通过解泊松方程计算了该材料的肖特基势垒的能带图，得到了该缺陷能级上电子的填充与发射随外加反向偏压变化的情况．并分析了用深能级瞬态谱（ＤＬＴＳ）对其进行测试所需的条件，以及与常规的ＤＬＴＳ测试结果的不同之处．提出了可同时对该缺陷上电子的发射和俘获过程进行ＤＬＴＳ测量的方法．实验测量结果表明，该高密度的界面缺陷的能级位置位于Ｅ_c－０．３０ｅＶ． 关键词：     

Inductively coupled plasma induced deep levels in epitaxial n-GaAs

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (E_c—0.046 eV, E_c—0.186 eV, E_c—0.314 eV. E_c—0.528 eV and E_c—0.605 eV) were detected. The metastable defect E_c—0.046 eV having a trap signature similar to E1 is observed for the first time. E_c—0.314 eV and E_c—0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.     

Atomic fluorescence mapping of optical field intensity profiles issuing from nanostructured slits, milled into subwavelength metallic layers

In this work, we report on the fabrication and characteristics of light-emitting diodes based on p-GaN/i-ZnO/n-ZnO heterojunction. A 30 nm i-ZnO layer was grown on p-GaN by rf reactive magnetron sputtering, then a n-ZnO was deposited by the electron beam evaporation technique. The current-voltage characteristic of the obtained p-i-n heterojunction exhibited a diode-like rectifying behavior. Because the electrons from n-ZnO and the holes from p-GaN could be injected into a i-ZnO layer with a relatively low carrier concentration and mobility, the radiative recombination was mainly confined in i-ZnO region. As a result, an ultraviolet electro-emission at 3.21 eV, related to ZnO exciton recombination, was observed in a room-temperature electroluminescence spectrum of p-i-n heterojunction under forward bias.     

Influence of growth temperature and post-annealing on an n-ZnO/p-GaN heterojunction diode

We report on an n-ZnO/p-GaN heterojunction diode fabricated from zinc oxide (ZnO) films at various growth temperatures (450, 500, 550, and 600 °C) by RF sputtering. The films were subsequently annealed at 700 °C in N₂ ambient. To investigate the influence of the growth temperature of n-ZnO films, the microstructural, optical, and electrical properties were measured using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and Hall measurements. The XRD pattern showed the preferred orientation along the c-axis (002) regardless of growth temperature. The PL spectra showed a dominant sharp near-band-edge (NBE) emission. Current–voltage (I–V) curves showed excellent rectification behavior. The turn-on voltage of the diode was observed to be 3.2 V for the films produced at 500 °C. The ideality factor of ZnO film was observed to be 1.37, which showed the best performance of the diode.     

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl₂O₄ spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×10²⁰ cm⁻³ (and carrier mobility of 28 cm²/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.     

Effect of MgZnO barrier layer on the UV emission of n-ZnO/p-Si heterojunction diodes

ZnO-based heterojunction light emitting diodes (LEDs) with MgZnO barrier layer had been fabricated on the p-Si substrate by metal-organic chemical vapor deposition (MOCVD) technology. The current-voltage (I-V) characteristics exhibited a typical p-n diode behavior. Both ultraviolet (UV) and visible emissions could be detected in the electroluminescence (EL) measurement. The result was compared with the EL spectrum of n-ZnO/p-Si heterojunction LED without MgZnO barrier layer. An improved light extraction efficiency by about 31% was realized owing to the current-blocking effect of MgZnO layer. The result indicated that MgZnO barrier layer can prevent the electrons as expected and realize electron-hole recombination in ZnO layer effectively.     

Photoluminescence and electroluminescence properties of ZnO films on p-type silicon wafers

A simplified n-ZnO/p-Si heterojunction has been prepared by growing n-type ZnO rods on p-type silicon wafer through the chemical vapour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380 nm. The electroluminescence spectrum of the n-ZnO/p-Si heterojunction shows a stable yellow luminescence band centred at 560 nm,which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.     

Current transport in ZnO/Si heterostructure grown by laser molecular beam epitaxy

The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15V 0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm 2 , respectively.     

Temperature dependence of the current-voltage characteristics of the Al/Rhodamine-101/p-Si(1 0 0) contacts

The current-voltage (I-V) characteristics of Al/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 280 to 400 K at 20 K intervals. A barrier height (BH) value of 0.817 eV for the Al/Rh101/p-Si/Al contact was obtained at the room temperature that is significantly larger than the value of 0.58 eV of the conventional Al/p-Si Schottky diode. While the barrier height Φ_b0 decreases the ideality factors (n) become larger with lowering temperature. The high values of n depending on the sample temperature may be ascribed to decrease of the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Therefore, at all temperatures, it has been seen that the I-V characteristics show three different regions, the ohmic behavior at low voltages, and the space charge limited current with an exponential distribution of traps at high voltages.     

基于氧化锌纳米线的紫外发光二极管

构建了基于n-ZnO纳米线/p-Si异质结的紫外发光二极管.ZnO纳米线准阵列采用水热法生长于重掺p型Si片上.此法简易，反应温度低，易于大规模生产；其产物ZnO纳米线结晶良好，以c轴为优势取向，光激发下的紫外荧光发射很强.二极管的电学接触采用聚合物填充的In阴极或以氧化铟锡(ITO)玻璃紧压形成阴极.它们的I-V特性体现出良好的二极管性质.在正向偏置电压驱动下，构建的发光二极管可稳定发射波长在387nm的较强的近紫外光和较弱的绿光. 关键词： ZnO纳米线 异质结 电致发光 水热法     

Direct-current piezoelectric nanogenerator based on p-Si/n-ZnO heterojunction

We have demonstrated a direct-current piezoelectric nanogenerator with a novel structure of p-Si/n-ZnO heterojunction. Low resistance p-type silicon chip, with a large number of nano-concaves on the surface, was utilized as a top electrode over the n-type ZnO nanorod arrays, forming a heterojunction nanogenerator. Piezoelectric current, with average singles about 1 nA, was generated from the heterojunction nanogenerator. Rectifying behavior of the p-Si/n-ZnO heterojunction in our piezoelectric nanogenerator was analyzed from the I–V curve and the energy band structure. Furthermore, output tests of reverse connection and two devices parallel connection clearly eliminate the effects from measurement system errors and confirms that the current is generated from the nanogenerator. Our research presents an approach to integrating a new type of nanogenerator using the silicon chip directly, without expensive Pt or Au coated on the electrode surfaces.     

Valence band contributions to photoluminescence excitation spectra of tightly bound holes in zincblende semiconductors

Photoluminescence excitation (PLE) spectra of deep acceptor states in ZnSe, for example the Cu-related luminescence band at ≈1.95 eV, contain a prominent excitation band at ≈3.25 eV. This band lies above the structure marking the lowest direct E_O band gap E_g by the spin-orbit splitting energy Δ of the valence bands at Γ. The higher energy feature is either absent or greatly de-emphasised in the PLE spectra of shallow acceptor states in ZnSe and of the oxygen iso-electronic trap in ZnTe, where the electron rather than the hole is tightly bound. However, a significant PLE component at E_g + Δ is observed for deep acceptor-like states in ZnTe, where Δ is ≈0.95 eV. Efficient PLE at E + Δ for luminescence from deep acceptor-like states is shown to be consistent with the extended wave-vector contributions to the bound state wave-functions of holes of binding energies ≈Δ.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.     

Transition metal impurities in silicon: New defect reactions

Recent investigations on transition-metal impurities in silicon emphasizing the effect of the combined diffusion of two transition metals are presented and briefly discussed. The electronic properties and basic thermal kinetics are analysed by DLTS. The conversion of a Pd-related multivalent defect atE _c-0.35 eV andE _c-0.57 eV to the Pd-related defect atE _c –0.22 eV is observed, and a Pd-Fe complex level atE _c –0.32 eV is identified. The annealing characteristics of the multivalent Rh levels atE _c-0.33 eV andE _c-0.57 eV are observed, and used to analyse the influence of prior Rh doping on the Au diffusion. A complex formed by the codiffusion of Au and Cu is observed atE _v+0.32eV andE _v+0.42 eV, and shown to exhibit bistable behavior as does a similarly produced Au-Ni complex observed atE _v + 0.35 eV andE _v+0.48 eV.