Donor and acceptor dynamics of phosphorous doped ZnO nanorods with stable p-type conduction: photoluminescence and junction characteristics

We employed temperature-dependent photoluminescence (PL) to explain the donor and acceptor dynamics in phosphorus doped stable p-type P:ZnO nanorods. The room temperature PL revealed good crystalline and optical quality of P:ZnO nanorods. The 10 K PL spectrum exhibited a dominant acceptor bound exciton (A0X) or donor bound exciton (D0X) emission corresponding to p- and n-type P:ZnO nanorods, respectively. The donor-acceptor-pair (DAP) transitions exhibited different thermal dissociation energies for the p- and n-type P:ZnO nanorods, suggesting their different quenching channels. The quenching of the DAP transitions of the p-type ZnO:P nanorods was associated with the thermal dissociation of the DAP into free excitons, while the DAP transition of the n-type ZnO:P nanorods was quenched through the thermal dissociation of the shallow donor into free electrons. The rectifying behavior of a p-n homojunction diode formed by the p-type P:ZnO nanorods on n-type ZnO film confirmed the p-type conduction of the P:ZnO nanorods.     

A photoluminescence study of vanadium-related defects in n-type, semi-insulating and p-type Cd(Zn)Te

A photoluminescence (PL) study of vanadium-related defects in semi-insulating and co-doped p-type and n-type CdTe:V crystals gives evidence of the presence of the V²⁺–Zn complex. In addition to the ³T₂(F)→³A₂(F) emission of V³⁺ near 0.5 eV and the ⁴T₂(F)→⁴T₁(F) transition of V²⁺ near 0.45 eV, two further luminescence bands are detected at higher energies. The first emission band (I), peaking around 0.8 eV, is correlated to the V²⁺–Zn complex and the second one (II), peaking around 0.6 eV, is attributed to the acceptor level introduced by the cadmium vacancies. Varying the zinc concentration in CdTe, we analyse the behaviour of the vanadium impurity charge state. We show that the V²⁺ internal transition decreases with zinc alloying due to the formation of the V²⁺–Zn complex. The emission bands related to isolated V_Cd are present with high intensity only in the p-type crystals, in which all the vanadium content is in the V³⁺ oxidation state, whereas, in the semi-insulating and n-type crystals, the PL spectrum is dominated by Emission I related to the V²⁺–Zn complex. The presence of this complex in the semi-insulating crystals used in photorefractive (PR) applications and the dominance of this complex over the optical properties of Cd(Zn)Te:V imply the contribution of this complex to the PR processes.     

Nitrogen-doped p-type ZnO thin films and ZnO/ZnSe p-n heterojunctions grown on ZnSe substrate by radical beam gettering epitaxy

We investigate the p-type doping in ZnO prepared by the method of radical beam gettering epitaxy using NO gas as the oxygen source and nitrogen dopant. Secondary ion mass spectroscopy measurements demonstrate that N is incorporated into ZnO film in concentration of about 8 × 10¹⁸ cm^− 3. The hole concentration of the N-doped p-type ZnO films was between 1.4 × 10¹⁷ and 7.2 × 10¹⁷ cm^− 3, and the hole mobility was 0.9-1.2 cm²/Vs as demonstrated by Hall effect measurements. The emission peak of 3.312 eV is observed in the photoluminescence spectra at 4.2  of N-doped p-type ZnO films, probably neutral acceptor bound. The activation energy of the nitrogen acceptor was obtained by temperature-dependent Hall-effect measurement and equals about 145 meV. The p-n heterojunctions ZnO/ZnSe were grown on n-type ZnSe substrate and have a turn-on voltage of about 3.5 V.     

P-type InP grown by liquid phase epitaxy with rare earths: not intentional Ge acceptor doping

InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP:Fe substrates with praseodymium added to the melt. Room temperature Hall effect measurements revealed p-type conductivity of the layers with the hole concentration 6×10¹⁴ cm⁻³ and mobility 150 cm² V⁻¹ s⁻¹. By measuring temperature dependence of the hole concentration the binding energy of the dominant acceptor was determined as 223 meV. A photoluminescence line was found at 1.195 eV, close to the previously estimated no-phonon line of Ge acceptor transitions in Ge doped n-type InP. It was concluded that Ge acceptors cause the p-type conductivity of the grown layers.     

Luminescence and reflectivity studies of undoped, n- and p-doped GaN on (0001) sapphire

GaN grown by three different methods (MOVPE, GSMBE and HVPE) have been studied using temperature (T) dependent reflectivity and photoluminescence (PL). Both non intentionally doped (MOVPE, GSMBE and HVPE), n- and p-doped samples (MOVPE and GSMBE) have been investigated. Reflectivity is used to obtain intrinsic transition energies. These energies vary with the amount of strain in the crystal. Growth parameters influencing this strain state are discussed. Using MOVPE (T_g≈1050°C) and GSMBE (T_g≈800°C), it is possible to grow samples whose low temperature PL spectra are dominated by free and bound excitons and their phonon replica. Intentional n-type doping up to 10²⁰ cm⁻³ is easily achieved with Si. For n10¹⁸ cm⁻³, the spectra broaden and exhibit a blue shift, attributed to band filling. p-Type doping has been attempted using Mg, C and Ca. Ca doping led to compensated samples. C doping using CCl₄ resulted in n-type samples, due to simultaneous oxygen incorporation in the layers; a strong enhancement of the 3.27 eV donor acceptor pair PL is also observed in this case. p-Type doping up to 10¹⁸ cm⁻³ has been achieved with Mg. With increasing densities, a deepening of the donor acceptor pair PL energy is observed. For high Mg doping, the spectra are dominated by a blue band in the 2.8 eV range, involving deep electron states.     

Properties of N-doped ZnO grown by DBD-PLD

N-doped ZnO thin films have been grown on sapphire substrates by dielectric barrier discharged pulsed laser deposition (DBD-PLD). Low temperature photoluminescence spectra of N-doped ZnO film verified the p-type doping status to find the acceptor-bound exciton peaks with the high resolution detection. At low temperature growth, the major defects in the N-doped ZnO film were the oxygen interstitials that can combine with N, so that the N played the role as an acceptor. On the other hand, the major defects in the samples processed at high temperature were oxygen vacancies with which N doesn't play the role as an acceptor. The acceptor binding energy of N acceptor was estimated to be about 105 meV.     

The effect of geometrical misfit dislocation on formation of microstructure and photoluminescence of Wurtzite GaN/Al2O3 (0001) films grown by low pressure metal-organic chemical vapor deposition

The incoherent GaN/sapphire interface and microstructure of GaN were observed by high resolution transmission electron microscopy. The most mobile 60° mixed-type dislocation is related to a structural metastability of the Wurtzite GaN film. In spite of the same feature of interband absorption, the photoluminescence mechanism is sensitive to deep level. A strong light emission from the bound exciton of Wurtzite GaN at 358 nm was observed in an n-type GaN sample with the GaN buffer layer. The donor–acceptor pair recombination at 380 nm with LO phonon replicas at 390 and 403 nm and the deep level at 559 nm were observed in both an undoped GaN sample with GaN buffer layer and an n-type GaN sample with AlN buffer layer. This optical behavior is sensitive to the Si doping and the type of buffer layer materials. The deep level emission along the dislocation line is suggested by the local band bending model providing the potential barrier of 0.63 eV by the space charge.     

Luminescence study of donors and acceptors in CdGeAs2

A photoluminescence (PL) study has been performed on a set of p-type bulk single crystalline samples of CdGeAs₂. At liquid-helium temperatures, a PL band peaking near 0.55 eV was observed in samples with enhanced absorption at 5.5 μm. This PL band was observed to vary as much as 40 meV in peak position in our sample set. The PL peak position depends on the net acceptor concentration (i.e., hole concentration) and the PL peak shifts to higher energy as the excitation intensity increases. We show that this behavior is well explained by the model of donor–acceptor pair (DAP) recombination in the presence of potential fluctuations.     

Low-temperature liquid-phase epitaxy growth from Ga–As–Bi solution

Measurements of Ga–As–Bi liquidus composition at 600 °C for Ga–Bi–GaAs range are reported. High quality GaAs layers and Al_0.28Ga_0.72As/GaAs single quantum well (SQW) structures with different well thicknesses are grown from a mixed Ga + Bi solvent by low-temperature liquid-phase epitaxy method. They are characterized by the Hall effect and photoluminescence (PL) measurements. Significant changes in the layer electrical properties are observed with varying the Bi content in the solution. The layers grown from a mixed solution with 20–30% Bi content are n-type with carrier concentration of 10¹⁴ cm^− 3 and mobility of 40 000 cm²/Vs at 77 K, while p-type high resistivity layers are obtained from a solution with more than 70% Bi content. PL spectra of the SQW structures grown from Ga + 25% Bi solution at 2 K show that the roughness at the interface is less than two monolayers.     

Systematic studies of impurities and nitrogen doping of photo-assisted MOVPE grown ZnSe using DESe, DMZn, TEN and TMSiN3

We present a study on the impurity incorporation and nitrogen doping of ZnSe epilayers grown by metalorganic vapour phase epitaxy (MOVPE) on (1 0 0)GaAs using dimethylzinc.triethylamine (DMZn.TEN), diethylselenium (DESe) and trimethylsilylazide (TMSiN3) as the Zn, Se and N precursors, respectively. Both pyrolytic and photoassisted MOVPE (PA-MOVPE) experiments have been carried out to identify the conditions for high purity growth. Characterization included both secondary ion mass spectrometry (SIMS) analysis to assess the incorporation of H, N and halogen impurities in the epilayers and 10 K photoluminescence (PL) measurements. SIMS elemental analysis of halogens in undoped ZnSe shows that the concentration of these impurities is of the order of 1×1015 cm-3, whilst the hydrogen concentration is about 2×1017 cm-3. In nominally undoped ZnSe epilayers an unexpectedly high level of nitrogen, ranging between 3×1016 cm-3 and 1×1018 cm-3, was found. The presence of N in undoped epilayers was confirmed by 10 K PL spectra, which are dominated by a N-related donor-acceptor-pair (DAP) band along with its LO-phonon replica and weaker bound exciton features in the near band-edge region. Finally, intentionally nitrogen doped ZnSe samples were grown by using TMSiN3 under PA-MOVPE conditions at 380 °C. SIMS analysis shows an efficient N incorporation up to 1×1020 cm-3 but increasing the N precursor partial pressure causes the growth rate to decrease together with an increase of the H content in the layers. 10 K PL spectra of doped ZnSe show a sharp nitrogen bound exciton peak in the near band-edge region along with dominant features ascribed to a free electron to acceptor transition at 2.710 eV and to a DAP band at around 2.695 eV, followed by their LO-phonon replica. © 1998 Chapman & Hall     

Optical and electrical properties of p-type AgInSnxS2−x (x = 0–0.04) thin films prepared by spray pyrolysis

AgInSn_xS_2−x (x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS₂. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn_xS_2−x (x < 0.2) resemble those of chalcopyrite AgInS₂. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn_xS_2−x (x < 2) thin films.     

ZnO薄膜的本征缺陷、p型掺杂及其新型功能器件

ZnO是一种宽禁带半导体材料(3.37eV),具有较高的激子结合能(60meV),室温下激子仍然存在。由于其结构特点及优异的光电性能,ZnO在微电子学、光电子学、集成光学和微电子机械系统等高技术领域有着广阔的应用前景,在国内外引起极大的关注。但本征的ZnO呈n型电导,p型ZnO的获得因较强的自补偿效应,存在较大困难,限制了其应用水平。针对ZnO目前的研究、就其本征缺陷、p型掺杂以及新型功能器件等方面做一简要评述。     

Electrical and optical characterization of Na: CuInS2 thin films grown by spray pyrolysis

The structural, electrical and optical properties of Na-doped CuInS₂ thin films grown by spray pyrolysis were studied. These films crystallized in the sphalerite structure of CuInS₂, and showed to contain traces of indium sulfide and CuIn₅S₈ as impurity phases. All films were In-rich and showed p-type conductivity. The film conductivity was strongly affected by Na-doping, which decreased from 10⁻² to 10⁻⁵ S/cm by increasing the [Na]/[Cu] ratio from 0.005 to 0.03 in the spray solution. The band gap energy was observed to increase, from 1.4 to 1.45 eV, with increasing the [Na]/[Cu] ratio. Our results suggested that Na could be an effective acceptor impurity in sprayed CuInS₂.     

Structural, optical and electrical properties of nitrogen ion implanted ZnO nanorods

This study examined the micro-structural and electrical properties of N+-ion-implanted ZnO nanorods. Nitrogen ions with energies of 10-90 keV and beam fluxes of 10(13)-10(16) ions/cm2 were implanted on vertically-aligned ZnO nanorods. Energy dispersive X-ray spectroscopy measurements showed that N+ ions were spread uniformly over the nanorods. Extended X-ray absorption fine structure measurements revealed that the implanted N+s had partially substituted for the oxygen sites. Photoluminescence measurements showed a neutral-donor bound exciton peak at 3.36 eV and a two-electron-satellite peak at 3.33 eV independent of the ion energy and flux. The I-V characteristic curves showed that the current density was not changed by the N+ ion energy and flux much. These results strongly suggested that the N ions substituted for the oxygen sites were neutral.     

Excitons emissions and Raman scattering of ZnO nanoparticles embedded in BaF2 matrices by reactive magnetron sputtering

ZnO nanoparticles embedded in BaF2 matrix were fabricated by rf magnetic sputtering technology. The optical properties of high quality ZnO nanoparticles, thermally post treated in a N2 atmosphere, were investigated by temperature-dependence photoluminescence measurement. Free exciton and localized exciton were observed at the low temperature. Free exciton peak was at 3.374 eV and localized exciton peak was at 3.420 eV, dominating the PL spectrum at 77 K. Free exciton transition was observed at 3.310 eV at room temperature, whereas the localized exciton transition was at 3.378 eV. The multiple-phonon Raman scattering spectrum showed that ZnO nanoparticles embedded in BaF2 matrix had a large deformation energy originated from lattice mismatch between ZnO and BaF2 matrix. Analysis of the fitting results from the temperature dependence of FWHM of ZnO exciton illustrated that the large value of gamma(ph) was good qualitative agreement with the large deformation potential.     

First-principle studies on the conductive behaviors of Ga,N single-doped and Ga–N codoped ZnO

We have performed first-principle calculations on the conductive behaviors of Ga, N single-doped and Ga–N codoped ZnO. According to the results, in the Ga single-doped case, with the comparatively smaller effective masses of electrons and the positive impurity formation energy, the fermi-level shifts upward into the conduction band, thus the n-type ZnO with good conductivity can be obtained. In both the N single-doped and Ga–N codoped cases, the fermi-levels shift downward into the valence band, indicating that p-type ZnO can be obtained by both of the methods. However, the holes’ effective masses in the codoping case are much smaller than those in the N single-doped case, and the formation energy in the codoping case is much larger than that in the N single-doped case, thus the p-type conductivity in the codoping case will be much better for its higher carrier mobility and higher acceptor solubility.     

Highly conducting doped poly-Si deposited by hot wire CVD and its applicability as gate material for CMOS devices

Highly conducting p- and n-type poly-Si:H films were deposited by hot wire chemical vapor deposition (HWCVD) using SiH₄+H₂+B₂H₆ and SiH₄+H₂+PH₃ gas mixtures, respectively. Conductivity of 1.2×10² (Ω cm)⁻¹ for the p-type films and 2.25×10² (Ω cm)⁻¹ for the n-type films was obtained. These are the highest values obtained so far by this technique. The increase in conductivity with substrate temperature (T_s) is attributed to the increase in grain size as reflected in the atomic force microscopy results. Interestingly conductivity of n-type films is higher than the p-type films deposited at the same T_s. To test the applicability of these films as gate contact Al/poly-Si/SiO₂/Si capacitor structures with oxide thickness of 4 nm were fabricated on n-type c-Si wafers. Sputter etching of the poly-Si was optimized in order to fabricate the devices. The performance of the HWCVD poly-Si as gate material was monitored using C–V measurements on a MOS test device at different frequencies. The results reveal that as deposited poly-Si without annealing shows low series resistance.     

Photoluminescence of Ga0.94In0.06As0.13Sb0.87 solid solution lattice matched to InAs

The lattice matched Ga_0.94In_0.06As_0.13Sb_0.87 quaternary solid solutions were grown by liquid phase epitaxy on (1 0 0) oriented InAs substrates from In rich melt. The p-type GaIn_0.06As_0.13Sb layers were intentionally undoped and their hole concentration was about p5×10¹⁶ cm⁻³, while n-type GaIn_0.06As_0.13Sb layers were slightly doped with Te and their electron concentration was about n10¹⁷ cm⁻³. Photoluminescence spectra exhibit single unresolved emission band in the spectral region from 0.65 to 0.8 eV for both types. Spectra were decomposed to elementary Gaussian components. The main mechanisms of radiative recombination were determined for both types of material.     

Study of steady-state photoluminescence of AgInSe2 crystals

The steady-state photoluminescence (PL) spectra of AgInSe₂ grown by the Hot-Press method have been examined. The broad peaks located at 1.19 eV and 1.16 eV are very likely to be the donor-acceptor-pair emissions. The energies of the donor levels participating in these emissions correspondingly are 25 eV and 50-52 meV, as found from the analyses of the activation energies of the PL intensity. The peaks observed in the obtained PL spectra in the band-edge region are attributed to free and bound excitons. The binding energy of the free exciton is estimated to be 29 meV.     

Properties of epitaxial ZnO:P films

Epitaxial ZnO:P films have been produced by annealing ZnP₂ substrates in atomic oxygen and characterized by X-ray diffraction, atomic force microscopy, Hall effect measurements, X-ray photoelectron spectroscopy, and photoluminescence measurements. The X-ray diffraction patterns of the films showed the 002 peak, indicating that their c axis was normal to the substrate surface. According to the Hall effect data, the layers were p-type, with a resistivity of ～20 Ω cm, hole mobility of ～9 cm²/(V s), and hole concentration of ～7.8 × 10¹⁷ cm^?3. The photoluminescence spectra of the ZnO:P films showed a peak at 3.356 eV (neutral acceptor bound exciton). Our results indicate that the ZnO:P films contain the P_Zn-2V_Zn defect complex as a shallow acceptor responsible for their p-type conductivity.