Zn Implantation Research Articles

Synthesis and transport properties of prospective photovoltaic systems related to CuInSe2 and CuGaSe2

Abstract Solid solutions in CuGaSe2–ZnSe and CuInSe2–ZnSe systems have been obtained by radio frequency heating. In order to prepare n-type phases based on CuGaSe2, p-type (CuGa)1−xZn2xSe4 and (CuIn)1−xZn2xSe4 (0.05⩽x⩽0.1) single crystals were doped by Ag, Hg, Cd, Zn implantation. The crystal structure of the solid solutions was studied by X-ray diffraction; the substitutors as well as the implantant valence states were analyzed using X-ray photoelectron spectroscopy. Hall effect, electrical conductivity, and the charge carrier mobility of an n-type zinc-implantated solid solution (CuGa)1−xZn2xSe4 and (CuIn)1−xZn2xSe4 (0.05⩽x⩽0.1) were studied.

Comparative study of as-implanted and pre-damaged ion-beam-synthesized ZnS nanocrystallites in SiO 2

The semiconducting ZnS nanocrystallites were synthesized by sequential high dose ion implantation of Zn and S in thermally grown SiO 2 on Si(1 0 0) and subsequent rapid thermal annealing (RTA). Some samples were pre-implanted with Ar ions in order to investigate the influence of radiation induced damage on the formation of ZnS nanocrystallites. The crystal structure of the ZnS crystallites, their size distribution and the concentration depth profile were analyzed by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and cross-sectional transmission-electron-microscopy (XTEM). The XRD results indicate, that the phase transition from cubic zinc blende to hexagonal wurtzite structure of ZnS nanocrystallites begins at temperatures below 1000 °C. The RBS results show a clear redistribution of Zn and S after RTA annealing. The concentration of Zn is seriously reduced due to strong diffusion towards deeper regions and the surface, while Ar pre-implantation partially suppressed the concentration loss of Zn. Moreover XTEM images show that the concentration profile, the radiation induced damage and the annealing temperature have strong influence on the resulting size distribution of formed ZnS nanocrystals.

Modification of the optical and luminescent properties of beryllium oxide crystals by implantation of Zn and Li ions

BeO single crystals were implanted at 295 K with either Zn or Li ions. Rutherford backscattering/channelling of helium ions was used to study lattice locations of the implanted Zn atoms. All the implanted atoms were found to occupy only regular positions of the BeO-lattice. Spectra of photoluminescence (PL), PL excitation, and X-ray luminescence from the Zn and Li implanted and non-implanted BeO crystals were studied in comparison with those for BeO crystals doped with Zn and Li. The PL-bands associated with radiation defects related to the Zn and Li implanted atoms were detected and identified. A theoretical study of the evolution of the implanted Zn and Li atoms in the BeO lattice was made using the molecular static and molecular dynamic techniques. The effect of the radiation defects related to the implanted Zn and Li ions on the optical and luminescence properties of BeO crystals has been discussed.

High Resistivity GaN Formed by Ion Implantation

ABSTRACTAdvanced high frequency devices using GaN-based semiconductor require the technology to form high resistivity regions with high thermal stability to electrically isolate the active elements from surroundings, as well as from the underlying substrate. The present paper describes the preparation of thermally stable, high resistivity GaN layers by ion implantation. It was confirmed that C or Zn implantation yielded high resistivity layers. In particular, Zn implantation yielded the layers with resistivity on the order of 1010 cm, which could be sustained at temperatures as high as 1000.

Formation of ZnAl2O4 and MgAl2O4 Spinel in Al2O3 by Ion Implantation

AbstractZnAl2O4 spinel has been formed in Al2O3 by ion implantation. Sequential implantation of Zn and 0 in overlapping profiles followed by annealing in Ar + H2 gives rise to a nearly continuous epitaxial layer of ZnAl2O4 oriented with (111) planes parallel to (0001) planes of Al2O3. If only Zn is implanted, then discrete bands of ZnAl2O4 oriented with (422) planes parallel to (0001) planes of Al2O3 are produced. By similar methods, oriented MgAl2O4 spinel also has been produced in Al2O3 by sequential Mg + O implantation.

The influence of the preliminary ion implantation in the ZnSe on the properties of the ZnOZnSe structures, obtained by the radical beam gettering epitaxy method

The structure and photoluminescence (PL) of ZnOZnSe structures obtained by Radical Beam Gettering Epitaxy method on the implanted ZnSe substrates has been investigated. It was found that the implantation of Zn + and Ar + and the post-implantation annealing in the stream of atomic oxygen results in the appearance of an intense band with the maximum in the range of 525–535 nm in the PL spectra. The centre responsible for this band is the complex centre including zinc vacancy. The interface boundary in the structure ZnOZnSe is sharp. The dimensions of the transient region are about 20 nm. The layers of zinc oxide are single crystals according to the data from electronic microscopy. The annealing of the samples implanted with oxygen at doses of 10 14–10 15 cm −2 results in the appearance of an intense band with a maximum at 560 nm in the PL spectra of ZnSe crystals. The implantation of O + ions with a dose of 10 19 cm −2 results in the formation of the ZnSe 1 − xO x solid solution layer. The erbium PL spectra in the structures are dependent, to a great extent, on the technological conditions of ZnSe crystals annealing in the atomic oxygen stream.

Ohmic contacts on p-In0.53Ga0.47As prepared by Zn implantation into Pd-based metallizations

A new technique is presented for the fabrication of low-resistivity Ohmic contacts on p-In0.53Ga0.47As doped below 1×1019 cm−3 consisting of dopant implantation into the contact metal and subsequent rapid thermal annealing. Zn-implanted and annealed Pd/Au/Pt/Au, Pd/LaB6/Au, and Pd/Ge contacts exhibit drastically lowerer contact resistivity in comparison to corresponding systems prepared without implantation. A resistivity decrease by approximately one and a half orders of magnitude is observed in cases of Pd/Au/Pt/Au and Pd/LaB6/Au contacts. The lowest value is found for Pd/Au/Pt/Au on p-In0.53Ga0.47As doped to 4×1018 cm−3 with 1×10−6 Ω cm2, whereas 1–2×10−5 Ω cm2 is obtained for Pd/Ge contacts on p-In0.53Ga0.47As doped to 7×1018 cm−3. The elemental redistribution and the interface morphology of annealed contacts have been studied with backside secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. No contact penetration and a planar interface are found in the case of Pd/Ge, whereas significant penetration of contact components into the semiconductor and nonplanarity of the interface are observed in Pd/Au/Pt/Au and Pd/LaB6/Au contacts. In contacts annealed at conditions for minimal resistivity the penetration depth is 200 and 105 nm, respectively. Implanted Zn is redistributed toward the contact interface during thermal processing. Thus the resistivity lowering is attributed to enhanced p-doping by Zn, which diffused from the contact into the underlying semiconductor. Residual implantation damage is discussed as the essential cause of the comparably high resistivity of implanted and annealed Pd/Ge contacts.

Non-alloyed, refractory metal contact optimization with shallow implantations of Zn and Mg

Refractory metal contacts to GaAs show great promise for stability during high temperature processing and for high reliability. In this paper, we report on a study of sputtered W and W-Si contacts to ion-implanted p-GaAs with both Zn and Mg implantations. This study focused on refractory contacts to shallow implanted contact layers that are suitable for devices such as junction field effect transistors and heterojunction bipolar transistors. The very different energy loss mechanisms of Zn and Mg ions result in different levels of implant damage, which is studied by varying the annealing temperatures and measuring the effects on contact and sheet resistances with the transmission line method. For the fabrication schemes investigated, the specific contact resistivity vs. annealing temperature values with implant doses form 1 × 1014 to 5 × 1015 cm-2 are found to vary from non- ohmic to 10-7ω cm2. Low resistance contacts to shallow (<800 Å) implanted layers are achieved.

Ion implantation effects in GaSb

The effects of ion implantation of Zn, Mg, Si, C, S and Se into n- and p-type GaSb have been studied. It is shown that low dose (5 × 10 13 cm −2) implantations of acceptor impurities, Zn, Mg and C at 60 keV are suitable for preparing good quality p-n GaSb diodes.

An all implanted self-aligned enhancement mode n-JFET with Zn gates for GaAs digital applications

An all implanted self-aligned n-channel JFET fabrication process is described where Zn implantation is used to form the p/sup +/ gate region. A refractory metal (W) gate contact is used to allow subsequent high temperature activation of the self-aligned Si source and drain implant. 0.7 /spl mu/m JFET's have a maximum transconductance of 170 mS/mm with a saturation current of 100 mA/mm at a gate bias of 0.9 V. The p/sup +//n homojunction gate has a turn on voltage of 0.95 V at a current of 1 mA/mm. The drain-source breakdown voltage is 6.5 V. Microwave measurements made at a gate bias of 1 V show an f/sub t/ of 19 GHz with an f/sub max/ of 36 GHz. These devices show promise for incorporation in both DCFL and complementary logic circuits. >

Thermal stability of Be-, Mg-, and Zn-implanted layers in GaAs for high-temperature device-processing technology

Results on the thermal stability of active acceptor layers in GaAs formed by Be, Mg, and Zn implantation are reported. Following rapid thermal annealing at 635 °C/35 s and 800 °C/15 s, the sheet carrier concentration is observed to remain constant after subsequent heat treatment below 600 °C for times up to 6 h. At and above this temperature, however, various changes are observed for different implants. These changes in the sheet electrical properties are observed to be reversible in the case of the Zn-implanted samples, where almost complete carrier recovery is observed after the samples were rapid thermal annealed at 800 °C/15 s after a long thermal anneal at 600 °C for 6 h.

Anneal Behavior of Zn Implanted InP : Furnace and Rapid Thermal Anneals

ABSTRACTIt is shown here that high-dose Zn implants in semi-insulating InP substrates, after conventional furnace anneals lead to the following anomalies : step-like atomic Zn and carrier distributions and the presence of electrically inactive Zn at all depths of the profiles.Zn anneal behavior is compared using conventional furnace anneals, and two different types of short-time anneals ; rapid furnace anneals(RFA)at ∼750°C with a rise-time of ∼ 50 s, and halogen lamp rapid thermal anneals (RTA)also at ∼ 750°C with a rise-time of ∼ 4 s. We have established that the Zn anomalous diffusion is an instantaneous phexomenon occuring during annealing transients. Also, we have further shown that RTA would help to smooth carrier profiles by removing the step in carrier (but not in atomic Zn) distribution.The properties of differently Zn co-implanted layers (Zn plus P, Zn plus In and Zn plus As) after RTA, and of P or In implanted Zn doped InP substrates after different anneals,have been studied. We have shown that the presence of electrically inactive Zn in the depth of the layers is a consequence of interaction between Zn atoms and defects. A simple model based on the density of damage deposited in the layer during implant, has been proposed and discussed.

Anomalous diffusion of acceptors in InP

Diffusion or implantation of acceptors into InP substrates are important techniques for forming device junctions. Some recent studies of Be, Zn, Mg, Mn implants revealed anomalous post-annealed profiles with relatively flat tails and abrupt leading edges, especially in Fe-doped semi-insulating substrates. Such deep tails are detrimental for obtaining shallow p-n junctions. The experiments to be described were carried out using SIMS on two sets of InP samples: Be-implanted, Mn- or Zn-doped substrates; Zn-implanted n-ty InP substrates whose electron concentrations ( n ) varied from 5 × 10 15 to 2 × 10 18 e cm −3 . After anneal, the study of the correlations between the movement of the dopants in the substrates and the Be, Cr, Zn implants show that the flat tails and the abrupt leading edges depend strongly on: i) the presence and the concentrations of impurities, or dopants, located on indium sites; ii) the solubility of the p-type in-diffusing element; iii) the occupancy of the phosphorus sites by other substitutional elements, as sulphur for example.

Ultra-Thin p+ Layers in GaAs

AbstractThe formation of shallow (0.05–0.2 μm) p+ layers in GaAs by pulse diffusion of Zn from a doped oxide source, thermal diffusion of Cd by vapor transport, or by low energy implantation of Cd, Mg, Be, Zn or Hg ions was investigated by electrochemical capacitance-voltage profiling, Secondary Ion Mass Spectrometry, Rutherford backscattering and Hall measurements. Hole densities in excess of 1019 cm−3 are obtainable by either Zn diffusion or acceptor implantation, though the high temperature cycle must be kept to ≤3 sec at (≤1000°C to prevent excessive redistribution of the acceptor dopants. Pulse diffusion at temperature °C leads to shallow regions with atomic concentrations above 1019 cm−3, but electrically active concentrations orders of magnitude less. These results are explained in terms of the unavailability of a sufficient density of vacancies at low temperatures.

Effect of ion implantation on electrochemical and surface properties of glassy carbon

Modification of glassy carbon (GC) surfaces was carried out by means of ion implantation of Zn +, Cd +, Ti +, and Ar +, in order to improve the characteristics of GC electrodes for electrochemical measurements. The concentration-depth profiles of the implanted element measured by secondary ion mass spectroscopy were in good agreement with theoretical values. The graphite lattice structure of the GC surface layer was changed to amorphous by the ion implantation. The implanted elements in the GC surface layer do not dissolve in the aqueous electrolyte solutions; this means a high stability of the surface material of the ion-implanted GC electrodes ensued. A redox reaction wave of hexacyano iron (II) and (III), as well as an oxygen reduction wave on the voltammograms are clearly detected by means of ion implanted GC electrodes, because of their lower residual currents and higher hydrogen overpotentials.

Metastable alloys of beryllium prepared by ion implantation

Surface alloys of beryllium metal have been prepared by high-fluence ion implantation of Ag, Ti, Zn, and Cu with solute concentrations ranging from a few tenths of a percent to tens of percent. Resulting surface layers were analyzed using the Rutherford backscattering/channeling technique and glancing angle X-ray diffraction methods. Solute depth profiles, lattice location, and precipitation behavior were derived and solvent lattice damage and recovery were studied as a function of fluence and annealing temperature.

Enhanced activation of Zn-implanted GaAs

Limitations on high level doping have been investigated for implanted Zn in GaAs. Fast diffusive redistribution during the annealing of heavy dose Zn implants generally leads to broader doped layers of lesser concentrations. Though such a redistribution can be prevented by short duration annealing of ∼1 s, this alone is not sufficient to increase the peak concentration. Significantly better activation can be obtained if an excess of As is also provided. It is found that coimplanting As with Zn in addition to short duration annealing provides layers with peak doping concentrations increased to levels approaching 1020 cm−3. Doping enhancement related to encapsulation and the outdiffusion of Ga into SiO2 has also been observed.

Ion implantation and diffusion of Zn in GaAs

Zn implantation (dose 5×1015 cm−2) and subsequent diffusion were carried out on GaAs wafers and on liquid-phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry. Annealing gave rise to Zn segregation at the surface or just below it and at a depth past the implantation maximum. The diffusion was much deeper and the damage recovery was much less with implantation through a nitride layer than with implantation directly into GaAs. This is explained in terms of recoil implantation of Si and N and of a smaller Ga vacancy concentration so that less trapping of interstitial Zn by such vacancies takes place. Surface segregation of Zn and differences in diffusion depth between samples with sputtered and CVD silicon nitride caps are ascribed to the effects of stress. Except in a surface layer, complete electrical activation and ideal Hall mobility values were found after annealing at 700 °C.

Zn-Implanted GaAs with minimized annealing redistribution

Redistribution associated with the annealing of high-dose Zn implants has been investigated in GaAs. Annealing times as short as ∼ 1 s have been implemented through direct radiant heating from an incoherent light source. It is shown that Zn can redistribute to depths of ∼ 1 µm even on annealing for only 10 s. Shallower layers (∼ 0.25 µm) and close to anticipated As-implanted depths require a further reduction in the annealing time to ∼ 1 s.

P+-n junction formed by dual implantation of Zn and As in GaAs junction field-effect transistors

The performance of a p+-n junction formed in GaAs by dual implantation of Zn and As was investigated. The transconductance in linear operation of the junction field-effect transistors (JFET's) in which the p+-gate was formed by the dual implantation was measured and analyzed on a simple one-dimensional model. As the dose of As was increased, the devices showed negatively shifted pinchoff voltage and higher transconductance. It was found that the co-implantation of As significantly decreased the width of the compensated layer in the junction, which improved the JFET's performance.