Effect of isochronal annealing on photoluminescence properties of Mn-implanted GaN

Mn ions were implanted into metal organic chemical vapour deposition (MOCVD)-grown GaN with dose ranging from 10¹⁴ to 5×10¹⁶ cm⁻². Isochronal annealing at 800 and 850 °C has been carried out after implantation of the samples. Photoluminescence measurements were carried out on the implanted samples before and after annealing. A peak found at 3.34 eV in the spectra of implanted samples after annealing at 850 °C is attributed to the stacking faults. Blue and green luminescence bands have been observed suppressed and an oxygen-related peak appeared at 3.44 eV in the PL spectra. The suppression of blue and green luminescence bands has been assigned to dissociation of V_GaO_N complex. Near-band-edge (NBE) peak exhibited a blue shift after 800 °C anneal and then red shift to restore its original energy position when annealed at 850 °C.     

Damage annealing behavior of Se implanted GaAs

High resolution Rutherford backscattering-channeling (RBS-C) and transmission electron microscopy (TEM) have been used to investigate the annealing behavior of Se implanted Cr-doped GaAs layers. Two distinct annealing stages were observed; one at 250°C which is associated with amorphous zone annihilation and/or onset of solid phase epitaxial growth and the other at about 400–500°C, depending on the dose, that can be related to the dissociation of microtwins. Above 500°C, the residual defects are primarily dislocation loops and precipitates. The calculated number of atoms associated with the precipitates has been found to correspond closely to the number of implanted atoms, implying 100% precipitation for the cases studied in this work. This could explain the poor or nonexistent electrical activation of Se after low temperature annealing (6̃00°C), even though good regrowth of the amorphous layer has taken place. Experiments with high purity GaAs produced the same result, as far as the observed residual damage was concerned, thus eliminating speculation about the involvement of Cr in the nucleation of microtwins. Transmission electron microscopy investigations of the amorphous-crystalline interface in the as-implanted samples failed to reveal any extended defects. In the present paper, we discuss various mechanisms that could be responsible for the formation of twins in low temperature annealed GaAs.     

Ion implantation of sulphur into GaAs,GaP and ge monocrystals

The possibility of using ion implantation to form high concentration junctions in semiconductors has been explored for the specific case of sulphur in GaAs, GaP and Ge. The effects of ion dose, ion energy, crystal orientation and target temperature have been investigated by means of radiotracers and sectioning techniques.

It is shown that high concentration junctions can be formed using an incident ion having high electronic stopping cross-section and implanted along the <110< channeling directions of the crystals. A large increase in junction concentration may be obtained when the GaAs and GaP crystals are maintained at 150 °C during the implantation process, but this is not the case with Ge. Rutherford back-scattering of 1 MeV He⁺ ions has been used to measure the ion-bombardment induced damage in the crystals and to show how this damage can be annealed by heating the crystal during the implantation. The annealing, at temperatures up to 150 °C, is most effective in GaAs and least effective in Ge.     

Hall effect and Raman analysis of residual damage and free electron concentration in Si-implanted GaAs: a quest for better doping efficiency

To tackle the problem of insufficient electrical activation of Si⁺ dopant in GaAs, we have studied a series of heavily Si-implanted and thermally annealed GaAs samples (two different doses, each implanted at three different temperatures and with two implantation rates). A comparative analysis of electrical and optical measurements was done on the same set of samples and correlated with implantation parameters. By temperature dependent Hall-effect measurements carrier density and carrier mobility were determined over the 20-300 K range. The mobility data were analyzed taking into account different scattering mechanisms.The implantation-induced initial damage was determined by Rutherford backscattering, whereas the amount of residual damage present in the samples after thermal annealing was estimated by Raman spectroscopy. Additionally, scattering by LO phonon-plasmon coupled modes was used to study the properties of the free electron gas in the implanted layer, including its depth distribution. Free carrier concentrations deduced from the analysis of the plasmon modes agree with the Hall-effect results. Multi-energy implantation in combination with higher implant temperature is suggested as a way to increase doping efficiency by reducing high local concentrations and lessen the probability of compensating defects formation.     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.     

Solid State Reaction of Ruthenium with 6H-SiC Under Vacuum Annealing and the Impact on the Electrical Performance of its Schottky Contact for High Temperature Operating SiC-Based Diodes

Thin films and Schottky diodes dots of ruthenium (Ru) on bulk-grown n-type-6-hexagonal-silicon carbide (6H-SiC) were annealed isochronally in a vacuum furnace at temperatures ranging from 500–1,000 °C. Rutherford backscattering spectroscopy analysis of the thin films showed formation of ruthenium silicide (Ru₂Si₃) at 800 °C, while diffusion of Ru into 6H-SiC commenced at 800 °C. Raman analysis of the thin films annealed at 1,000 °C showed clear D and G carbon peaks which was evidence of formation of graphite. At this annealing temperature, the Schottky contact was observed to convert to an ohmic contact, as evidenced by the linearity of current–voltage characteristic, thereby, rendering the diode unusable. The transformation from Schottky contact to ohmic contact is attributed to graphite formation at the interface.     

Photoluminescence of sodium-implanted zinc selenide

Luminescence measurements indicate that Na acceptors implanted into ZnSe become optically active after annealing at 500°C. The spectra show a strong Na dependence for both the R series band and the I^Y₁ exciton line. In this work Ne-implanted and unimplanted samples were annealed and measured with the Na-implanted material to isolate defect-induced spectral features. Several new bands resulting from radiation damage are reported, along with annealing properties of the defect bands and Na-related luminescence.     

Radiation damage by implanted ions in GaAs and GaP

Abstract

The production of lattice disorder in GaAs and GaP by Te ions up to 40 keV has been investigated. For GaAs the build up of damage with implanted ion dose is linear until a saturation level is reached. For Gap, two linear regions are evident; a slow build up of damage to ?15 per cent of the saturation level, followed by a faster rate of increase up to the final 100 per cent level. Radiation annealing, for GaP samples, both by the heavy ion beam during implantation and by the helium beam during back-scattering measurements has been observed. The annealing temperatures required for re-ordering the lattice depend on the percentage of damage present. Samples damaged up to the saturation level require annealing at ?500°C, whilst 300°C is sufficient for samples damaged to ?50 per cent of the saturation value.     

Photoluminescence study of native defects in annealed GaAs

Low temperature (6°K) photoluminescence measurements have been performed on GaAs annealed under various conditions, to study defects generated by outdiffusion of the constituent atoms. Several defect-related luminescence peaks have been observed and associated with Ga and As outdiffusion. The outdiffusion of these elements during annealing to 850°C in vacuum and with Ga or As overpressure and SiO₂ coatings is studied by monitoring the intensities of these peaks.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

Effects of thermal annealing on the interband transitions of single and vertically stacked InAs/GaAs self-assembled quantum dots

Photoluminescence (PL) measurements have been carried out to investigate the annealing effects in one-period and three-periods of InAs/GaAs self-assembled quantum dots (QDs) grown on GaAs substrates by using molecular beam epitaxy. After annealing, the PL spectra for the annealed InAs/GaAs QDs showed dramatic blue shifts and significant linewidth narrowing of the PL peaks compared with the as-grown samples. The variations in the PL peak position and the full width at half-maximum of the PL peak are attributed to changes in the composition of the InAs QDs resulting from the interdiffusion between the InAs QDs and the GaAs barrier and to the size homogeneity of the QDs. These results indicate that the optical properties and the crystal qualities of InAs/GaAs QDs are dramatically changed by thermal treatment.     

Electron microscopy studies of void swelling and annealing of voids in aluminium irradiated with aluminium ions

Abstract

MgO single crystals implanted with Au⁺ ions (180 keV, 6 10¹⁶-10¹⁷ ions cm^?2) and annealed at temperatures between 25°C and 1100°C, have been analysed—by optical spectrophotometry—by Rutherford back-scattering (to confirm the effective presence and to study the distribution profile of Au atoms), and by TEM and X-ray diffraction (to identify the phases precipitated by thermal treatment).

Thermal annealing between 550°C and 1100°C produced an optical absorption band located between 565 nm and 600 nm. This band can be attributed to a fee Au precipitate with diameter varying from 50 to 200 Å. Larger metallic colloids 1000 Å are in simple orientation with the matrix.

Annealing at temperatures higher than 500°C produces a supplementary optical absorption located at 425 nm. This band can be attributed to Au plasma resonance.

After annealing for 15 min at 1100°C, a new phase is detected by X-ray diffraction and TEM and identified as Au₃Mg alloy with hexagonal structure.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

不同退火条件对纳米多孔氧化铝薄膜光致发光的影响

以草酸为电解液,采用二次阳极氧化法制备出了纳米多孔氧化铝薄膜,经不同退火温度和退火气氛处理氧化铝薄膜后,通过分析其光致发光光谱得出：相同的退火气氛中, 退火温度T≤600 ℃ 时,T=500 ℃具有最大的光致发光强度;退火温度T≥700 ℃时,随着退火温度的升高,样品的发光强度增大。在不同的退火气氛中,多孔氧化铝薄膜随着退火温度的升高,发光峰位改变不同,即在空气中退火处理后,随着退火温度的升高,发光峰位蓝移,而在真空中退火处理后,发光峰位并不随退火温度的升高而变化;通过对1 100 ℃高温退火处理后的氧化铝薄膜的光致发光曲线的高斯拟合,可以看出,经退火处理后的多孔氧化铝,主要存在三个发光中心,发光曲线在350～600 nm范围内对应三个发射峰, 发射波长分别为387,410,439 nm。相同的退火温度下,空气中退火得到的氧化铝薄膜的光致发光强度大于真空中退火处理后的氧化铝薄膜。基于实验结果,结合X射线色散能谱(EDS)、红外反射光谱等表征手段,探讨了多孔氧化铝薄膜的发光机制,并对经过不同退火条件得到的多孔氧化铝薄膜的光致发光特性的改变做出了合理的解释。     

Nature of room-temperature ferromagnetism from undoped ZnO nanoparticles

ZnO nanoparticles were synthesized by a sol–gel calcination process following being annealed in air at 400, 600, 800 and 1000°C. X-ray diffraction pattern and X-ray photoelectron spectroscopy show that all the samples present a typical wurtzite structure and no other impurity phases are observed. Room-temperature ferromagnetism from all the samples is confirmed by the vibrating sample magnetometer measurements, which shows that the RTFM decreases with the annealing temperature increasing from 400 to 800°C, and then became larger for the sample annealed at 1000°C. According to the Raman scattering spectra and electron paramagnetic resonance, the RTFM of samples annealed at 600, 800 and 1000°C might be related to the oxygen vacancy related defects. However, the RTFM from the sample annealed at 400°C, presenting nearly the same value as that of the sample annealed at 1000°C, could originate with the interstitial zinc defects associated with XPS and photoluminescence analyses.     

Luminescence lifetimes in quartz: dependence on annealing temperature prior to beta irradiation

It is well known that the thermal history of a quartz sample influences the optically stimulated luminescence sensitivity of the quartz. It is found that the optically stimulated luminescence lifetime, determined from time resolved spectra obtained with pulsed stimulation, also depends on past thermal treatment. For samples at 20°C during stimulation, the lifetime depends on beta dose and on duration of preheating at 220°C prior to stimulation for quartz annealed at 600°C and above, but is independent of these factors for quartz annealed at 500°C and below. For stimulation at higher temperatures, the lifetime becomes shorter if the sample is held at temperatures above 125°C during stimulation, in a manner consistent with thermal quenching. A single exponential decay is all that is required to fit the time resolved spectra for un-annealed quartz regardless of the temperature during stimulation (20–175°C), or to fit the time resolved spectra from all samples held at 20°C during stimulation, regardless of annealing temperature (20–1000°C). An additional shorter lifetime is found for some combinations of annealing temperature and temperature during stimulation. The results are discussed in terms of a model previously used to explain thermal sensitisation. The luminescence lifetime data are best explained by the presence of two principal luminescence centres, their relative importance depending on the annealing temperature, with a third centre involved for limited combinations of annealing temperature and temperature during stimulation.     

Lattice location and thermal annealing behaviour studies of GaAs single crystals implanted with Co-atoms

Co-atoms have been implanted into n-type GaAs single crystals up to a dose of 2×10¹⁵ atoms/cm². Mössbauer Spectroscopy was used together with Proton Induced X-ray Excitation and Rutherford Backscattering Spectrometry in Channeling geometry to study the recovery of the GaAs-crystal from the implantation damage and the final lattice locations of the Co-atoms. Epitaxial regrowth of the GaAs was found to take place in the annealing temperature region from 300°–450°C. At 900°C rapid thermal annealing an epitaxial Co-phase was found at the surface with the Co-atoms partially blocking the GaAs <110> channel.     

磷离子注入速率对4H-SiC(0001)晶格恢复与电阻率降低的影响

高剂量的磷离子注入4H-SiC(0001)晶面，注入速率从1.0×1012到4.0×1012 P+ cm-2s-1变化，而注入剂量固定为2.0×1015 P+ cm-2。室温注入，1500oC的高温下退火。利用光荧光和拉曼谱分析注入产生的晶格损伤以及退火后的残余缺陷。通过霍耳测试来分析注入层的电学性质。基于上述测试结果，发现通过减小磷离子的注入速率，极大地减少了注入层的损伤及缺陷。考虑到室温注入以及相对较低的退火温度(1500 oC)，在注入速率为1.0×1012 P+ cm-2s-1及施主浓度下为4.4×1019 cm-3的条件下，获得了非常低的方块电阻106 Ω/sq。     

C and Si ion implantation and the origins of yellow luminescence in GaN

We have studied the influence of C and Si ion implantation with different implantation doses on yellow luminescence (YL) from GaN. Three kinds of GaN samples were used. In their as-grown states, #1 samples had strong YL, #2 samples had no YL, while #3 samples had weak YL. Our experimental results show that: (i) after annealing at 950 °C, the YL intensity for Si ion implanted #1 sample decreased with increasing implantation dose, while that for C ion implanted #1 sample exhibited a reverse rule; (ii) for #2 samples, C ion implantation produced much stronger YL than Si ion implantation did after annealing at 950 °C; (iii) the YL intensity sequence for Si ion implanted and 950 °C annealed #1, #2, and #3 samples was consistent with that for the unimplanted #1, #2, and #3 samples. However, the YL intensity sequence for the C ion implanted and 950 °C annealed #1, #2, and #3 samples reversed with that for the unimplanted ones. In order to explain all these phenomena, we suggested a physical model which claims that the deep C center is another important origin of YL in GaN, and during C ion implantation, the C ion prefers to combine with a V_Ga to form a C_Ga. PACS 78.55.-m, 85.40.Ry, 68.55.Ln     

ion implantation of bismuth into GaP. I. photoluminescence

Photoluminescence from the bismuth isoelectronic trap implanted into GaP is investigated for various ion doses and annealing conditions. A thin coating of silicon oxide is found to be essential to prevent thermal decomposition of the implanted surface during annealing. In isochronal anneal studies the intensity of the Bi luminescence increases rapidly between 650 and 800°C. For 200 keV implants, the dose for maximum luminescence is ～3.5 × 10¹² ions/cm², corresponding to an average concentration of ～10¹⁸/cm³. However, for the optimum dose and anneal, one observes only ～10 per cent of the light intensity expected from the estimated number of substitutional ions, and the emitting ions are situated in lattice sites with strong local strain. This strain is evident in the photoluminescence spectrum by the appearance of a strong no-phonon line which results from an otherwise forbidden transition when strain or an external field are present. The luminescence data are correlated with channeling experiments reported in a companion paper.