Influence of an increase in the implantation dose of erbium ions and annealing temperature on photoluminescence in AlGaN/GaN superlattices and GaN epitaxial layers

Room-temperature photoluminescence (PL) has been studied in AlGaN/GaN superlattices and GaN epitaxial layers implanted with 1-MeV erbium at a dose of 3 × 10¹⁵ cm^?2 and annealed in argon. The intensity of PL from Er³⁺ ions in the superlattices exceeds that for the epitaxial layers at annealing temperatures of 700–1000°C. The strongest difference (by a factor of ～2.8) in PL intensity between the epitaxial layers and the superlattices and the highest PL intensity for the superlattices are observed upon annealing at 900°C. On raising the annealing temperature to 1050°C, the intensity of the erbium emission from the superlattices decreases substantially. This circumstance may be due to their thermal destruction.     

Influence of rapid high-temperature anneals on the photoluminescence of erbium-doped GaN in the wavelength interval 1.0–1.6 µm

The influence of rapid-anneal conditions and subsequent coimplantation of oxygen ions on the photoluminescence of erbium ions implanted with an energy of 1 MeV and dose of 5×10¹⁴ cm⁻² in MOCVD-grown GaN films is investigated. The erbium photoluminescence intensity at a wavelength ∼ 1.54 μm increases as the fixed-time (15 s) anneal temperature is raised from 700 °C to 1300 °C. The erbium photoluminescence intensity can be increased by the coimplantation of oxygen ions at anneal temperatures in the indicated range below 900 °C. The transformation of the crystal structure of the samples as a result of erbium-ion implantation and subsequent anneals is investigated by Raman spectroscopy. Fiz. Tekh. Poluprovodn. 33, 3–8 (January 1999)     

Nature of the edge electroluminescence peak in the Si:(Er,O) diode breakdown mode

Electroluminescence (EL) of erbium-and oxygen-doped Si:(Er,O) diodes at λ=1.00–1.65 μm has been studied in the p-n junction breakdown and forward current modes. The EL was measured at room temperature from the front and back surfaces of the diodes. A peak corresponding to the absorption band edge of silicon was observed in the EL spectra of some diodes in the p-n junction breakdown mode. The peak is associated with the injection of minority carriers from the metal contact into silicon, with subsequent band-to-band radiative recombination. The band-to-band recombination intensity increases sharply on reaching a certain current density that depends on the fabrication technology. This threshold current density decreases with the temperature of post-implantation annealing of Si:(Er,O) diodes increasing in the range 900–1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 4, 2002, pp. 453–456. Original Russian Text Copyright ? 2002 by Emel’yanov, Nikolaev, Sobolev.     

Effects of defect,carrier concentration and annealing process on the photoluminescence of silicon pn diodes

Silicon pn diodes were fabricated by ion implantation of B and P ions with different doses and subsequent annealing processes. Room temperature photoluminescence (PL) were investigated and the factors affecting the PL intensity were analyzed. Results show that both kinds of pn diodes have PL peak centered at about 1140 nm. Dislocation loops resulted from ion implantation and annealing process may enhance the light emission of silicon pn diode due to its band quantum confinement effect to carriers. The luminescence intensity depends on the carrier concentrations in the implantation region. It should be controlled at the range of 1–6×10¹⁶ cm⁻³. Moreover, the PL intensities of pn diodes with furnace annealing (FA) are higher than those with rapid thermal annealing, and the annealing temperature range for FA is 900–1100 °C.     

Effect of annealing on electrical properties of radio-frequency-sputtered ZnO films

We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800–1,000°C. The electron concentration increased with annealing temperature reaching 1.4×10¹⁹ cm^?3 for 1,000°C. Mobility also increased, however, reaching its maximum value 64.4 cm²/V · sec for 950°C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 Å). After annealing at 900°C, the leakage current (at ?5 V reverse bias) decreased from 2.2 × 10^?7 A to ～5.0 × 10^?8 A after annealing at 900°C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950°C. The leakage current decreased from 2.0×10^?4 A to 3.0×10^?7 A at ?10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher.     

Microwave Annealing of High Dose Al<Superscript>+</Superscript>-implanted 4H-SiC: Towards Device Fabrication

High-purity semi-insulating 8° off-axis 〈0001〉 4H-SiC was implanted with Al⁺ at different doses and energies to obtain a dopant concentration in the range of 5 × 10¹⁹–5 × 10²⁰ cm^?3. A custom-made microwave heating system was employed for post-implantation annealing at 2,000 °C for 30 s. Sheet resistance and Hall-effect measurements were performed in the temperature range of 150–700 K. At room temperature, for the highest Al concentration, a minimum resistivity of 3 × 10^?2 Ω cm was obtained, whereas for the lowest Al concentration, the measured resistivity value was 4 × 10^?1 Ω cm. The onset of impurity band conduction was observed at around room temperature for the samples implanted with Al concentrations ≥3 × 10²⁰ cm^?3. Vertical p ⁺-i-n diodes whose anodes were made by 1.5 × 10²⁰ cm^?3 Al⁺ implantation and 2,000 °C/30 s microwave annealing showed exponential forward current–voltage characteristics with two different ideality factors under low current injection. A crossover point of the temperature coefficient of the diode resistance, from negative to positive values, was observed when the forward current entered the ohmic regime.     

Dislocation-related luminescence in single-crystal silicon subjected to silicon ion implantation and subsequent annealing

Implantation of silicon ions with an energy of 100 keV at a dose of 1 × 10¹⁷ cm^?2 into n-type floatzone Si does not lead to the formation of an amorphous layer. Subsequent annealing in a chlorine-containing atmosphere at 1100°C gives rise to dislocation-related luminescence. The intensity of the dominant D1 line peaked at a wavelength of ～1.54 μm grows as the annealing time is increased from 15 to 60 min.     

Low-temperature growth of silicon epitaxial layers codoped with erbium and oxygen atoms

The fabrication technology and properties of light-emitting Si structures codoped with erbium and oxygen are reported. The layers are deposited onto (100) Si by molecular beam epitaxy (MBE) using an Er-doped silicon sublimation source. The partial pressure of the oxygen-containing gases in the growth chamber of the MBE facility before layer growth is lower than 5 × 10^?10 Torr. The oxygen and erbium concentrations in the Si layers grown at 450°C is ～1 × 10¹⁹ and 10¹⁸ cm^?3, respectively. The silicon epitaxial layers codoped with erbium and oxygen have high crystal quality and yield effective photoluminescence and electroluminescence signals with the dominant optically active Er-1 center forming upon postgrowth annealing at a temperature of 800°C.     

Influence of irradiation with swift heavy ions on multilayer Si/SiO2 heterostructures

The influence of Xe ions with an energy of 167 MeV and a dose in the range 10¹²-3 × 10¹³ cm^?2 on heterostructures consisting of six pairs of Si/SiO₂ layers with the thicknesses ～8 and ～10 nm, correspondingly, is studied. As follows from electron microscopy data, the irradiation breaks down the integrity of the layers. At the same time, Raman studies give evidence for the enhancement of scattering in amorphous silicon. In addition, a yellow-orange band inherent to small-size Si clusters released from SiO₂ appears in the photoluminescence spectra. Annealing at 800°C recovers the SiO₂ network, whereas annealing at 1100°C brings about the appearance of a more intense photoluminescence peak at ～780 nm typical of Si nanocrystals. The 780-nm-peak intensity increases, as the irradiation dose is increased. It is thought that irradiation produces nuclei, which promote Si-nanocrystal formation upon subsequent annealing. The processes occur within the tracks due to strong heating because of ionization losses of the ions.     

Effect of annealing on the optical and structural properties of GaN:Er

The effect of annealing on the optical and structural properties of gallium nitride layers grown by metalorganic chemical vapor deposition and implanted with 0.8 to 2.0-MeV erbium ions at doses of (1−4)×10¹⁴ cm⁻² is investigated. Additional implantation of 0.11 to 0.28-MeV oxygen ions at doses of (1−4)×10¹⁵ cm⁻² is performed on some samples. Measurements of the Rutherford backscattering of protons show that amorphization of the gallium nitride layers does not occur at the erbium implantation doses investigated. The formation of erbium-related luminescence centers which emit at 1.54 μm ends before the defect structure of the implanted layers is restored during a postimplantation anneal in the temperature range 700–1300 °C. Fiz. Tekh. Poluprovodn. 33, 674–676 (June 1999)     

Resistivity changes of heavily-boron-doped CVD-prepared polycrystalline silicon caused by thermal annealing

Heavily-boron-doped polycrystalline Si films were deposited at 600°C on thermally grown SiO₂ by the thermal decomposition of SiH₄-BCl₃-H₂ mixture. Resistivity changes with isochronal or sequential annealing were systematically examined. Temperature dependence of equilibrium saturation carrier concentration was determined at 800 ～ 1100°C. Since as-deposited polycrystalline Si is in the super-saturated state, carrier concentration decreases from the super-saturated to equilibrium saturation value by annealings over 700°C for poly Si doped with over 2 × 10²⁰ cm^?3 resulting in anomalous resistivity change. Carrier concentration changes reversibly between saturation values with sequential annealing and is determined by the last annealing temperature when the annealing time is long enough. Mobility increases with annealing temperature, however, less increase is found for heavily doped poly Si, which is attributed to the suppression of grain growth caused by electrically inactive Si-B compounds.     

Photoluminescence in silicon implanted with erbium ions at an elevated temperature

Photoluminescence spectra of n-type silicon upon implantation with erbium ions at 600°C and oxygen ions at room temperature and subsequent annealings at 1100°C in a chlorine-containing atmosphere have been studied. Depending on the annealing duration, photoluminescence spectra at 80 K are dominated by lines of the Er³⁺ ion or dislocation-related luminescence. The short-wavelength shift of the dislocation-related luminescence line observed at this temperature is due to implantation of erbium ions at an elevated temperature. At room temperature, lines of erbium and dislocation-related luminescence are observed in the spectra, but lines of near-band-edge luminescence predominate.     

Lateral schottky GaN rectifiers formed by Si<Superscript>+</Superscript> ion implantation

Type conversion of p-GaN by direct Si⁺ ion implantation and subsequent annealing was demonstrated by the fabrication of lateral Schottky diodes. The Si⁺ activation percentage was measured as a function of annealing time (30–300 sec) and temperature (1,000–1,200°C), reaching a maximum of ∼30% for 1,200°C, 2-min anneals. The resulting n-type carrier concentration was 1.1×10¹⁸ cm⁻³ for a moderate Si⁺ ion dose of ∼2×10¹⁴ cm⁻². The lateral Schottky diodes displayed a negative temperature coefficient of −0.15 V·K for reverse breakdown voltage.     

Formation and study of buried SiC layers with a high content of radiation defects

Protons with energy E=100 keV were implanted with doses ranging from 2×10¹⁷ to 4×10¹⁷ cm^?2 into 6H-and 4H-SiC n-type samples at room temperature. The samples were subjected to various types of postimplantation heat treatment in the temperature range 550–1500°C. The parameters of the samples were studied by measuring the capacitance-voltage and current-voltage characteristics and by analyzing the photoluminescence spectra. Blistering on the surface of the sample is observed after annealing the samples at a temperature of 800°C only after implantation of protons with a dose of ≤3×10¹⁷ cm^?2. A decrease in the resistivity of the compensated layer sets in after annealing at a temperature of ～1200°C and is completed after annealing at a temperature of ～1500°C. A drastic decrease in the photoluminescence intensity is observed after implantation for all types of samples. Recovery of the photoluminescence intensity sets in after annealing at temperatures ≥800°C and is complete after annealing at a temperature of 1500°C.     

Tunnel light-emitting Si:(Er,O) diodes with a short rise time of Er3+ electroluminescence under breakdown conditions

Si:(Er,O)-based tunnel light-emitting diodes were fabricated and exhibited the shortest ever recorded characteristic rise time for erbium electroluminescence. This is due to the formation of Er-related centers with an effective excitation cross section for erbium ions of ∼7×10⁻¹⁶ cm² and an excited-state lifetime of ∼17 μs. The lifetime of the first excited state of erbium ions after turning off the reverse current was measured for the first time; this lifetime is associated with Auger energy transfer to free electrons in the electrically neutral region of the diode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 8, 2000, pp. 965–969. Original Russian Text Copyright ? 2000 by Emel’yanov, Sobolev, Trishenkov, Khakuashev.     

Electrical Characteristics of Ti/Al Ohmic Contacts to Molecular Beam Epitaxy-Grown N-polar n-type GaN for Vertical-Structure Light-Emitting Diodes

We investigated the electrical properties of Ti(30?nm)/Al(200?nm) contacts to molecular beam epitaxy-grown N-polar n-GaN with different carrier concentrations. Samples with carrier concentration of 1.2?×?10¹⁸?cm^?3 showed nonohmic behaviors when annealed at 300°C, but ohmic at 500°C and 700°C. All samples with carrier concentration of 2.0?×?10¹⁹?cm^?3 exhibited ohmic behavior. x-Ray photoemission spectroscopy (XPS) results showed that, for samples with carrier concentration of 1.2?×?10¹⁸?cm^?3, the Ga 2p core levels shift to lower or higher binding energy upon annealing at 300°C or above 500°C, respectively. Scanning transmission electron microscopy (STEM) results showed that, for samples with carrier concentration of 1.2?×?10¹⁸?cm^?3, a wurtzite AlN layer (??2?nm thick) formed at the metal/GaN interface when the samples were annealed at 500°C. An interfacial wurtzite AlN layer also formed upon annealing at 700°C, but its thickness was ??4?nm. Based on the XPS and STEM results, the ohmic contact formation and degradation mechanisms are described and discussed.     

Strain evolution and dopant activation in P-lmplanted metastable pseudomorphic Si(100)/Ge0.12Si0.88

A metastable Ge_0.12Si_0.88 layer 265 nm thick was deposited pseudomorphically on a Si(100) substrate and then implanted with 100 keV phosphorus ions at room temperature for doses of 5 × 10¹³/cm² to 1.5 × 10¹⁵/cm². The ions stop within the epilayer (projected range ∼125 nm). MeV⁴He backscattering/channeling spectrometry, transmission electron microscopy, and double-crystal x-ray diffractometry were used to characterize the damage and strain in the films. The samples were subsequently annealed in high vacuum from 400-800°C for 30 min at each temperature. For the nonamorphized samples (doses of 5 and 10 × 10¹³/cm²), most of the implantation-induced damage and strain disappear after annealing at 400-550°C, but the implanted P ions activate poorly. After annealing at 700-800°C, near complete activation is achieved but the strain relaxes. For the amorphized samples (dose of 1.5 × 10¹⁵/cm²), the amorphous GeSi regrows by solid-phase epitaxy and the dopants are ∼100% activated after annealing at 550°C, but the regrown GeSi relaxes with a high density of dislocations. The strain relaxes more extensively upon annealing in an implanted sample than in a nonimplanted one, other conditions being equal. This effect is more pronounced at higher ion doses, probably due to the increased amount of damage introduced at high doses. On leave from Yonsei University, Seoul 120-749, Korea     

Electrical and optical activation studies of Si-implanted GaN

Comprehensive and systematic electrical and optical activation studies of Si-implanted GaN were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 5×10¹⁵ cm^?2 at room temperature. The samples were proximity-cap annealed from 1050°C to 1350°C with a 500-Å-thick AlN cap in a nitrogen environment. The optimum anneal temperature for high dose implanted samples is approximately 1350°C, exhibiting nearly 100% electrical activation efficiency. For low dose (≤5×10¹⁴ cm^?2) samples, the electrical activation efficiencies continue to increase with an anneal temperature through 1350°C. Consistent with the electrical results, the photoluminescence (PL) measurements show excellent implantation damage recovery after annealing the samples at 1350°C for 20 sec, exhibiting a sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak. The mobilities increase with anneal temperature, and the highest mobility obtained is 250 cm²/Vs. The results also indicate that the AlN cap protected the implanted GaN layer during high-temperature annealing without creating significant anneal-induced damage.     

Electrical and optical characterization studies of lower dose Si-implanted AlxGa1−xN

Electrical and optical activation studies of lower dose Si-implanted Al_xGa_1?xN (x=0.14 and 0.24) have been made systematically as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 1×10¹⁴ cm^?2 at room temperature. The samples were proximity cap annealed from 1,100°C to 1,350°C with a 500-Å-thick AlN cap in a nitrogen environment. Nearly 100% electrical activation efficiency was obtained for Al_0.24Ga_0.76N implanted with a dose of 1 × 10¹⁴ cm^?2 after annealing at an optimum temperature around 1,300°C, whereas for lower dose (≤5×10¹³ cm^?2) implanted Al_0.24Ga_0.76N samples, the electrical activation efficiencies continue to increase with anneal temperature up through 1,350°C. Seventy-six percent electrical activation efficiency was obtained for Al_0.14Ga_0.86N implanted with a dose of 1 × 10¹⁴ cm^?2 at an optimum anneal temperature of around 1,250°C. The highest mobilities obtained were 89 cm²/Vs and 76 cm²/Vs for the Al_0.14Ga_0.86N and Al_0.24Ga_0.76N, respectively. Consistent with the electrical results, the photoluminescence (PL) intensity of the donor-bound exciton peak increases as the anneal temperature increases from 1,100°C to 1,250°C, indicating an increased implantation damage recovery with anneal temperature.     

Electronic properties of p-GaN(Mg) irradiated with reactor neutrons

The effect of irradiation with full-spectrum reactor neutrons and predominantly fast reactor neutrons (up to a fluence of 8 × 10¹⁸ cm^?2) on the electrical properties of epitaxial p-GaN(Mg) films at different initial doping levels (in the range of hole concentrations p = 10¹⁷–10¹⁹ cm^?3) is analyzed. It is found that neutron irradiation induces an increase in the resistivity of the initial material to 10¹⁰ Ω cm at 300 K. It is shown that, at high neutron fluences, the resistivity of the material decreases because of the hopping conduction of charge carriers over radiation defect states. The study of isochronous annealing at 100–1000°C reveals stages of donor-defect (100–300°C, 500–700°C, 750–850°C) and acceptor-defect (300–500°C, 650–800°C) annealing in the neutron-irradiated p-GaN(Mg) samples.