An investigation of Au/Mn contacts to p-type InP

The performance of a Au/Mn contact metallization to p-type InP has been reported. Electrical resistance measurements done on annealed contacts have been correlated to the accompanying microstructural changes, by means of electron microscopy and X-ray diffraction techniques. Manganese was found to react readily with the underlying InP, leading to the formation of Mn₂P followed by MnP. Subsequent outward diffusion of indium towards the gold layer led to the formation of Au₃In, which replaced the original gold layer. Inward diffusion of gold resulted in the formation of an Au-In-Mn ternary phase at the MnP-InP interface. This phase may have supplied the necessary manganese for InP doping required to lower the contact resistance. A minimum resistance of 6 x 10^-4Ωcm² was obtained.     

Characterization of ohmic contacts to InP

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as ohmic contacts are presented. The layers were heat treated at temperatures up to 550°C and were examined with Auger electron spectroscopy. For contact to n-type InP three thin film systems were investigated: gold, nickel and a composite Ni/Au/Ge layer. Nickel was found to produce ohmic behavior in the Ni/Au/Ge/InP system with a minimum specific contact resistance r_c of 3×10^?5 Ω cm² for a net doping of 3×10¹⁶ cm^?3. For contact to p-type InP a film consisting of Au/Mg was investigated. For heat treatment of the Au/Mg/InP system above 350°C, r_c decreased as the temperature of the heat treatment increased and the surface morphology exhibited increasing signs of alloying at higher temperatures. The smoothest surface was obtained at 446°C for 50 min with r_c≈1×10^?4Ω cm² for a net doping of 6×10¹⁷ cm^?3.     

Interrupted Mg doping of GaN with MOCVD for improved p-type layers

Uniformity doping, δ-doping and growth-interruption doping to produce gallium nitride (GaN): Mg has been investigated by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). It was demonstrated by electrical, optical, and surface studies that films produced by growth-interruption-Mg-doping produce the best crystal quality, this doping method increasing self-compensation because of the incorporation of additional impurities during the interruption period. Mg-δ-doping employs GaN:Mg/UGaN superlattices valence band edge oscillation to enhance hole concentration leading to significantly reduced p-type resistivity, enhanced hole mobility. This doping method also leads to improved surface morphology.     

Indium doped silver oxide thin films prepared by reactive electron beam evaporation technique: electrical properties

The indium doped silver oxide thin films have been prepared at 275 °C on soda lime glass and silicon substrates by reactive electron beam evaporation technique; the deposition rate has been varied (by varying the electron beam current) in the range 0.94–16.88 nm/s keeping the oxygen flow rate constant. These films are polycrystalline. The electrical resistivity for these films decreases with increasing deposition rate. The AIO films prepared with a deposition rate of 5.7 nm/s show near p-type conductivity. The work function has been measured on these films by contact potential method using Kelvin Probe. The surface morphology of the films has been evaluated using atomic force microscopy (AFM). The roles of indium doping and oxygen vacancies in the electrical properties of these films have been analyzed; the ionized impurity scattering is the dominant mechanism controlling the electrical conduction in these films.     

The effect of Cr barrier on interfacial reaction of Au/Zn/Au/Cr/Au contacts to p-type InGaAs/InP

Alloy-type metal is widely used to reduce contact resistance in optoelectronic devices. Among the alloy-types, Au/Zn is one of the most common metallization systems. In this paper, we studied the alloy morphology of p-InP/p-InGaAs/Au/Zn/Au/Cr/Au systems. We found that the amount of Au-Zn alloy depended upon the thickness of the Cr layer. When Cr thickness was reduced to 135 Å, both Au-rich and GaAs-rich excessive compound formation started to occur. The Au diffusion punched through the InGaAs layer and penetrated into the InP. Comparison of Au/Zn/Au and Au/Zn/Au/Cr/Au suggested that the top Au layer maybe very influential during the alloy reaction. The Au-Zn alloy was significantly less in the Au/Zn/Au than that in the Au/Zn/Au/Cr/Au.     

Preparation of P-type indium phosphide films by close space vapor transport

InP films have been grown by close space transport employing 0.8 mol% PCl₃ in H₂. For deposition on InP single crystals, 700C source and 650C substrate temperatures produced epitaxial films on (100), polycrystalline films on (111)A, and powdery layers on (111)B. Growth rates are 6 to 10 |Gmm/hr on (100) InP and ~50 μm/hr on (111)A InP. Regardless of InP source doping, deposits exhibit net donor concentrations of 5×10¹⁷ to 1×10¹⁸cm^?3. Zn doping with 0.02 to 0.5 mol% Zn(C₂H₅)₂ in the gas phase resulted in partially compensated p-InP with net acceptor concentrations up to 7×10¹⁸cm^?3. Polycrystalline films have been grown on Mg-coated carbon or molybdenum substrates at 700C source and 590C substrate temperatures. Growth rates lie between 40 and 50 μm/hr. Substantial recrystallization and grain growth are observed after 2 day anneals at 950C under 5 atm of phosphorus.     

Study by AES and EELS spectroscopies of antimony and phosphorus evaporated on massive indium and on cleaned InP

In this paper, we give some results related to interaction mechanism between the elements V such as antimony or phosphorus with the metal indium. We used both powerful spectroscopy methods the Auger electron spectroscopy (AES) and the electron energy loss spectroscopy (EELS) for which the spectra were recorded in direct mode N(E). The antimony was evaporated on pure In metal or on cleaned InP surface involving the In metal because of its cleaning by the argon ion bombardment at low energy 300 eV. The antimony flow composed of Sb₄ species arrived with a thermal energy on the In metal surface. Such an energy was sufficient to their diffusion into the In matrix because of the low melting point of In metal (123 °C). A nucleation phenomenon occurred between Sb₄ and the In metal to form small islands of antimony metal in bulk. Further antimony evaporation enabled to increase the size of these islands towards the surface. However, the antimony evaporated on cleaned InP reacted chemically with the In metal distributed on the InP surface to form a thin layer of InSb. The inner stoichiometric layers of InP and the size of Sb₄ species and also the stability of InP versus the temperature impeded the interdiffusion phenomenon of antimony to occur deeply into the InP matrix. The InSb layer played the role to stabilise the surface of the InP compound versus the heating at 450 °C and the electron irradiation of 4 KeV energy. But, the phosphorus evaporation on In metal or on cleaned InP led to form chemical bonds InP. The phosphorus flow included chemical species P and P₂ with a thermal energy able to stimulate the chemical reactivity process between indium and phosphorus to form the InP compound.     

Electrical properties of the CdS/InP solar cell for photovoltaic applications

n-CdS/p-InP solar cells have been prepared by deposition of n-CdS thin films using thermal evaporation technique onto p-type InP <100>. The I–V characteristics of the CdS/InP heterojunctions in dark condition were studied in the 298–350 K temperatures range for charge transport mechanism investigation. It has been established that in the entire temperatures range, the charge transport mechanism is determined by recombination processes in the depletion region. The CdS/InP heterojunction solar cells obtained using this technique and characterized under illumination condition have showed a conversion efficiency of 11% at I_sc = 10 mA/cm², V_oc = 0.7 V.     

Preparation of transparent,electrically conducting ZnO film from zinc acetate and alkoxide

Very uniform and transparent zinc oxide thin films doped with aluminium and indium were fabricated by the dip-coating technique using solutions prepared by the ethanolamine method. As starting materials, zinc acetate and zinc n-propoxide were used. Zinc acetate and propoxide are soluble in PrⁱOH in the presence of diethanolamine, although they are hardly soluble without the amine. The prepared solutions were very stable and suitable for dip-coating. Zinc oxide was crystallized by heating above 500 °C, and doping of aluminium and indium retarded the crystallization. The electrical resistivity of the film was decreased by doping with aluminium and indium. The lowest resistivity of 2 × 10^–2 cm was obtained by post-coating treatment in a nitrogen atmosphere.     

Remote p-doping of InAs nanowires

We report on remote p-type doping of InAs nanowires by a p-doped InP shell grown epitaxially on the core nanowire. This approach addresses the challenge of obtaining quantitative control of doping levels in nanowires grown by the vapor-liquid-solid (VLS) mechanism. Remote doping of III-V nanowires is demonstrated here with the InAs/InP system. It is especially challenging to make p-type InAs wires because of Fermi level pinning around 0.1 eV above the conduction band. We demonstrate that shielding with a p-doped InP shell compensates for the built-in potential and donates free holes to the InAs core. Moreover, the off-current in field-effect devices can be reduced up to 6 orders of magnitude. The effect of shielding critically depends on the thickness of the InP capping layer and the dopant concentration in the shell.     

Formation of wurtzite InP nanowires explained by liquid-ordering

We report an in situ surface X-ray diffraction study of liquid AuIn metal alloys in contact with zinc-blende InP (111)(B) substrates at elevated temperatures. We observe strong layering of the liquid metal alloy in the first three atomic layers in contact with the substrate. The first atomic layer of the alloy has a higher indium concentration than in bulk. In addition, in this first layer we find evidence for in-plane ordering at hollow sites, which could sterically hinder nucleation of zinc-blende InP. This can explain the typical formation of the wurtzite crystal structure in InP nanowires grown from AuIn metal particles.     

Growth and characterization of indium phosphide nanowires on transparent conductive ZnO:Al films

The epitaxial growth of indium phosphide nanowires (InP NWs) on transparent conductive aluminum-doped zinc oxide (ZnO:Al) thin films is proposed and demonstrated. ZnO:Al thin films were prepared on quartz substrates by radio frequency magnetron sputtering, then InP NWs were grown on them by plasma enhanced metal organic chemical vapor deposition with gold catalyst. Microstructure and optical properties of InP nanowires on ZnO:Al thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), photoluminescence and Raman spectroscopy at room temperature. SEM shows that randomly oriented and intersecting InP nanowires were grown to form a network on ZnO:Al thin films. Both wurtzite (WZ) and zincblende (ZB) structures coexist in the random orientation InP NWs on ZnO:Al thin film had been proved by XRD analysis. XPS result indicates Zn diffusion exists in the InP NWs on ZnO:Al. The photoluminescence spectra of InP nanowires with Zn diffusion present an emission at 915 nm. Zn diffusion also bring effect on Raman spectra of InP NWs, leading to more Raman-shift and larger relative intensity ratio of TO/LO.     

Effect of indium doping on zinc oxide films prepared by chemical spray pyrolysis technique

We report the conducting and transparent In doped ZnO films fabricated by a homemade chemical spray pyrolysis system (CSPT). The effect of In concentration on the structural, morphological, electrical and optical properties have been studied. These films are found to show (0 0 2) preferential growth at low indium concentrations. An increase in In concentration causes a decrease in crystalline quality of films as confirmed by X-ray diffraction technique which leads to the introduction of defects in ZnO. Indium doping also significantly increased the electron concentrations, making the films heavily n type. However, the crystallinity and surface roughness of the films decreases with increase in indium doping content likely as a result of the formation of smaller grain size, which is clearly displayed in AFM images. Typical optical transmittance values in the order of (80%) were obtained for all films. The lowest resistivity value of 0.045 Ω-m was obtained for film with 5% indium doping.     

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 × 10⁻² Ω cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide.     

Charge transport mechanism and photovoltaic behaviour of undoped and I2 doped tris (1,10 phenanthroline) iron (II) complex (TPFe) thin film devices

Tris (1,10 phenanthroline) iron (II) or Fe (Phen)²⁺ ₃, a metal-to-ligand charge transfer (MLCT) type complex (TPFe), was employed in the form of thin films, for the fabrication of Schottky diodes, Al/ TPFe/ITO, where ITO is indium tin oxide. The effect of iodine doping on the electrical behaviour has been emphasized. The diodes exhibit a rectification effect which improves on iodine doping. The diodes can be classified as MIS Schottky diodes with a graded dopant profile. The current-voltage (J-V ), and capacitance-voltage (C-V ) characteristics, the photoaction spectra of the devices and the absorption spectra of the complex, reveal that both doped and undoped complexes behave as a p-type organic semiconductor which form a Schottky barrier with Al and an ohmic contact with ITO. Various electrical and photovoltaic parameters were determined from the detailed analysis of J-V and C-V characteristics and these are discussed in detail. The effect of I_{_2} doping on the rectification and photovoltaic properties is also discussed.     

Violet GaN based light emitting diodes fabricated by metal organics vapour phase epitaxy

For almost 2 decades, p-doping of GaN was not feasible. Since the ionisation energy of any acceptor species is >200 meV, the hole concentration obtained by p-doping is only one hundredth of the acceptor impurity concentration. Mg has been so far the most typical dopant used for p-type GaN. In metal organics vapour phase epitaxy (MOVPE), the precursor was the bismethylcyclopentadienyl Mg, (MeCp)₂Mg. However, two severe drawbacks must be overcome. The Mg precursor and ammonia react in the vapour phase to give solid particles. In addition, H is incorporated during the growth process, therefore, a post growth annealing is required. The Mg doped GaN samples studied were grown by MOVPE on (0001) oriented sapphire substrates. With proper design of the growth chamber and thermal annealing, doping densities up to 2×10¹⁸ cm⁻³ have been reached. Photoluminescence (PL) and photocapacitance data reveal that in addition to the shallow acceptors, deep states are most likely related to Mg complexes. n-Doping is straightforward. Si is easily introduced via silane and allows a free carrier concentration up to 10¹⁹ cm⁻³ to be reached. Henceforth p–n junctions and light emitting diodes were achievable.     

Transparent conductive indium-doped zinc oxide films prepared by atmospheric pressure plasma jet

Atmospheric-pressure plasma processing has attracted much interest for industrial applications due to its low cost, high processing speed and simple system. In this study, atmospheric-pressure plasma jet technique was developed to deposit indium-doped zinc oxide films. The inorganic metal salts of zinc nitrate and indium nitrate were used as precursors for Zn ions and In ions, respectively. The effect of different indium doping concentration on the morphological, structural, electrical and optical properties of the films was investigated. Grazing incidence X-ray diffraction results show that the deposited films with a preferred (002) orientation. The lowest resistivity of 1.8 × 10^− 3 Ω cm was achieved with the 8 at.% indium-doped solution at the substrate temperature of 200 °C in open air, and average transmittance in the visible region was more than 80%.     

Growth of p-type ZnO thin films by using an atomic layer epitaxy technique and NH3 as a doping source

Nitrogen-doped, p-type ZnO thin films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C₂H₅)₂ [Diethylzinc, DEZn], H₂O and NH₃ as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 210 Ω cm with a hole concentration of 3.41 × 10¹⁶ cm^− 3. Low temperature-photoluminescence analysis results support that the nitrogen ZnO after annealing is a p-type semiconductor. Also a model for change from n-type ZnO to p-type ZnO by annealing is proposed.     

Analysis of interface states in Au/ZnO/p-InP (MOS) structure

Zinc oxide (ZnO) film was deposited on p-type InP substrate by means of radio frequency magnetron sputtering technique and thus the Au/ZnO/p-InP (MOS) structure was fabricated. The crystal structure and surface morphology of ZnO film deposited on InP were characterized by X-ray diffraction and atomic force microscopy, respectively. The analysis of interface states of the structure is studied using admittance (Y?=?G?+?iωC) measurements at room temperature. It is observed that the capacitance and conductance measurements change with frequency. This change is attributed to the presence of interface states. To determine the interface state density (N_ss), the high-low frequency (C_HF–C_LF) capacitance, Hill–Coleman and conductance methods were used. The N_ss values obtained from these methods are in agreement with each other. Furthermore, the effect of the series resistance (R_s) on admittance measurements was investigated. Thus, the obtained results suggest that the prepared structure can be used in various electronic applications.     

Improved Al/Si ohmic contacts to p-type 4H-SiC

An AlSi-based ohmic contact with a new composition is reported in this paper. AlSi(2%)Ti(0.15%) contacts are formed by evaporation on p-type 4H-SiC grown by liquid phase epitaxy (LPE) and annealed in the temperature range from 700 to 950°C. The ohmic behaviour has been checked by I–V characteristics and the contact resistivity has been measured by the linear transmission-line-model (TLM) method. The dependence of the contact resistivity on the annealing conditions has been studied. An ohmic behaviour has been established at 700°C while the lowest contact resistivity value of 9.6×10⁻⁵ Ω cm² has been obtained after annealing at 950°C. The thermal stability of both Al/Si/SiC and AlSiTi/SiC contacts at a temperature of 600°C has been studied. It has been found that the AlSiTi/SiC contacts are stable for 100 h at this ageing temperature while the Al/Si/SiC contacts deteriorate after 24 h.