Laser annealing of ainc implanted GaAs

GaAs samples implanted with 1.10¹⁵ zinc ions/cm³ have been annealed using pulses from a ruby laser operating in the freely generated mode. The percentage electrical activities and peak carrier concentrations were found to depend on the implant temperature, the laser energy density and the number of pulses. The maximum hole concentration measured was about 1.10²⁰ cm^?3 following irradiation with four pulses of 3 J/cm². Significant residual damage remained after single pulse irradiation at this energy density value. However, the carrier mobilities were similar to values for good single crystal GaAs.     

Rapid Thermal annealing of si implanted GaAs

Rapid thermal annealing (RTA) with incoherent light from tungsten lamps shows high potential relative to the conventional furnace annealing (FA) to activate the implanted dopant. Due to the short time annealing, it could completely eliminate the re-diffusion of dopant and host atom. For the Si implantation with dose of 2 × 10¹⁴ cm², the electrical activity of 78% for RTA was higher than that of the FA. But for this short time, some defects measured by deep level transient spectroscopy (DLTS) were hard to remove. A two-step annealing was suggested by the combination of high temperature RTA (1000° C) and FA (700° C). After the post-FA, the defects would be removed to a great extent, and the electrical activity of dopant also increased. With the dose of 2 x 1013 cm^-2, the activity attained after the two step annealing was 92.5%, which may be the highest value according to our knowledge for rapid thermal annealing on Si ion implanted GaAs.     

Pulsed laser annealing of zinc implanted GaAs

Samples of n type GaAs implanted with 1015Zn+/cm2 at room temperature were irradiated with a ruby laser of pulse length 0.8 ms. For samples coated with Si3N4 a laser energy of 1.5?2.5 J/cm2 produced electrical activity of 40?50% of the implanted dose. Peak hole concentrations up to about 7 × 1019 cm?3 were measured. Uncoated samples irradiated with similar laser energies were not electrically active.     

Characterisation of Se implanted layers for GaAs FETs

Results on doping profile, uniformity of doping and mobility for Se implanted LEC grown semi-insulating GaAs substrates are presented as a function of Se ion energy and annealing temperature. SiO₂, RF sputtered Si₃N₄ and Ga₂O₃+Al are used as encapsulating layers. Surface effects (stress and damage) on doping efficiency of implanted Se ions are also included.     

Role of substrate in electrical properties of GaAs implanted layers

The variation of implantation efficiency in different semi-insulating GaAs materials is shown to be correlated with he purity of the starting substrate, i.e. its Cr concentration and more especially its value of ND?NA (shallow levels). This last value appears to be a key parameter in the electrical properties of implanted layers.     

Laser annealing of GaAs implanted with low doses of selenium ions

GaAs samples were implanted with 100–400 keV, 10¹²–10¹⁴/cm²Se⁺ ions and annealed using undiffused and diffused pulsed ruby-laser beams with the samples held at various temperatures.

The resulting surface and structural defects as observed by various microscopic and spectroscopic methods are related to measured electrical properties of implanted GaAs, and the causes of the observed poor and lack of electrical activation of samples identified.

Laser irradiation of samples (T ≈ 516°C) induces surface damage in the form of regular parallel broken lines with a periodicity of about 0.69 μm, the wavelength of the ruby laser.

A diffused laser beam (0.5 J/cm²) reduces surface vaporisation and eliminates periodic surface structures. The measured electrical properties are still poor.     

Electron beam annealing of zinc implanted GaAs to control profile broadening

Highly doped P+ layers have been obtained by using multiply scanned electron beam annealing. The diffusion of the zinc was controllable at temperatures above 900°C if anneal times were less than 3 s.     

Electrical and cathodoluminescence measurements on ion implanted donor layers in GaAs

GaAs has been doped by the ion implantation of silicon, sulphur, selenium and tin. After annealing at 700°C, the layers were n-type in all cases but with the heavier ions, selenium and tin, it was necessary to implant above room temperature. Van der Pauw measurements showed that for all the impurities the surface concentration of free electrons as a function of ion dose reached a maximum of approximately 10¹³ electron/cm² with an average Hall mobility of 2000 cm²/V sec. The spatial distributions of active donors were obtained from both differential Hall measurements and capacitance measurements on reverse biased Schottky barriers. The maximum carrier density measured was 10¹⁸/cm³ at the peak of the distribution of tin ions implanted at 200°C. With selenium and tin implants the concentration and mobility of free electrons and the depth of the donor distribution were dose dependent. The cathodoluminescence spectra from implanted layers were dominated by broad low energy bands due to recombination at defects. A V_Ga-Si complex was thought to be responsible for one of the most intense bands at 1·18 eV. The results indicate that under certain conditions both defects and impurities migrate into the substrate.     

On the behaviour of buried oxygen implanted layers in highly doped GaAs

Highly doped GaAs substrate material (doping level 10¹⁸ cm⁻³) has been implanted with 350 keV O⁺ ions with doses of 10¹⁴ – 10¹⁶ cm⁻² to produce high resistivity layers which are stable at high temperatures. LPE growth of flat GaAs epilayers onto the implanted wafers was achieved up to doses of about 1 × 10¹⁵ O⁺/cm² and 5 × 10¹⁵O⁺/cm² for RT and 200°C implants, respectively. N-o-n and p-o-n structures (o: oxygen implanted) were fabricated in which breakdown voltages of up to 15 V were obtained. Examples for application of this isolation technique are shown.     

Redistribution of Al in implanted SiC layers as a result of thermal annealing

The experimental Al concentration profiles formed on implantation of Al into SiC at room temperature with subsequent high-temperature annealing are analyzed. It is shown that, at doses above the amorphization threshold, the profiles exhibit a number of specific features: a shift of the maximum of the distribution, accumulation of dopants at the surface, and formation of box-shaped profiles. To describe quantitatively the redistribution of Al dopants in the SiC layers implanted with high doses, the segregation-diffusion model is suggested for the first time. The model takes into account segregation of dopants between the α and c phases during solid-state epitaxial crystallization followed by diffusion of dopants and their evaporation from the surface The formation of box-shaped Al profiles as a result of short-term thermal annealing is attributed to the origination of highly damaged single-crystal and polycrystalline SiC layers in the recrystallized region, with a high diffusion coefficient of dopants, and to the suppression of the enhanced transient diffusion in the remaining single-crystal part of the implanted layer.     

Effect of ion dose rate on rapid laser annealing of implanted GaAs

Short-duration laser annealing of localized regions on P⁺ ion-implanted GaAs wafers has been examined for various doses and dose rates by micro-Raman scattering and Rutherford backscattering measurements. Time required for complete annealing of ion-induced defects varies from 5 ms to 1 s, corresponding to the implanted dose and rate. It is found that the amount of produced defects is enhanced by implantation with higher dose rates and that defects produced with higher dose rates are more easily annealed by the laser irradiation during short durations within a certain dose range.     

GaAs planar gunn devices with sulfur-ion implanted n layers

Planar type Gunn effect devices have been fabricated by sulfur-ion implantation into the Cr doped semi-insulating GaAs substrates. The high doping efficiency as 90% was obtained as a result of long heat treatment. The mobility of the sulfur-ion implanted n layers with average carrier concentration of 4 × 10¹⁶cm^?3 was 5200 cm²/Vsec at room temperature and 12,000 cm²/Vsec at 77 K. The minimum gate trigger voltage of the Gunn effect digital devices was 100 mV. Sulfur-ion implanted Gunn effect devices have shown superior current drop ratio dependence on doping-depth product, compared to the devices prepared from the epitaxial layer.     

Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO₂ layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si₄ bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm^?1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520 cm^?1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm^?1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature.     

Formation of photoluminescence centers during annealing of SiO2 layers implanted with Ge ions

Photoluminescence (PL), Raman scattering, and the Rutherford backscattering of α-particles were used to study the formation of the centers of radiative-recombination emission in the visible region of the spectrum on annealing of the SiO₂ layers implanted with Ge ions. It was found that the Ge-containing centers were formed in the as-implanted layers, whereas the stages of increase and decrease in the intensities of PL bands were observed following an increase in the annealing temperature to 800°C. The diffusion-related redistribution of Ge atoms was observed only when the annealing temperatures were as high as 1000°C and was accompanied by formation of Ge nanocrystals. However, this did not give rise to intense PL as distinct from the case of Si-enriched SiO₂ layers subjected to the same treatment. It is assumed that, prior to the onset of Ge diffusion, the formation of PL centers occurs via completion of direct bonds between the neighboring excess atoms, which gives rise to the dominant violet PL band (similar to the PL of O vacancies in SiO₂) and a low-intensity long-wavelength emission from various Ge-containing complexes. The subsequent formation of centers of PL with λ_m～570 nm as a result of anneals at temperatures below 800°C is explained by agglomeration of bonded Ge atoms with formation of compact nanocrystalline precipitates. The absence of intense PL following the high-temperature anneals is believed to be caused by irregularities in the interfaces between the formed Ge nanoc-rystals and the SiO₂ matrix.     

Patterning by rapid thermal annealing of GaAs layers grown on diluted nitride QWs

The structural characterization of hole patterns on GaAs cap layers grown on GaInNAs quantum wells (QWs) created by rapid thermal annealing is shown in this work. The effect of annealing temperature on the hole size, as well as the impact of the ion density present during the growth of the QW on the formation of this hole pattern, is presented. Structural (atomic force, scanning electron and transmission electron microscopy) and optical characterization (cathodoluminescence) of the samples is presented. The structure of the planes forming the walls and base of these holes is proposed.     

Redistribution of implanted oxygen in GaAs

We show that implanted oxygen in GaAs has two different thermal behaviours depending on the implantation dose. In the case of low doses, below 1014 oxygen-cm?2 oxygen diffuses very quickly at 900°C. In the case of high doses, above 1014 oxygen-cm?2, oxygen piles up around its projected range during annealing. This should be due to the formation of precipitates. The presence of substrate impurities in the nucleation process is not suspected.     

Current transport in fluorine implanted GaAs

Effects of fluorine implantation in GaAs have been investigated by electrical characterization. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². The effect of fluorine implantation on current-voltage (I-V) characteristics of Schottky diodes was significant. Carrier compensation was observed after implantation by the improved I-V characteristics. The lower dose implanted samples showed thermionic emission dominated characteristics in the measurement temperature range of 300 to 100K. The starting wafer and the low dose implanted samples after rapid thermal annealing (RTA) showed similar I-V properties with excess current in the lower temperature range dominated by recombination. The higher dose implanted samples showed increased excess current in the whole temperature range which may result from the severe damage-induced surface recombination. These samples after RTA treatment did not recover from implantation damage as in the low dose implantation case. However, very good I-V characteristics were seen in the higher dose implanted samples after RTA. The influence of the higher dose ion implantation was to produce more thermal stability. The results show the potential application of fluorine implantation in GaAs device fabrication.     

Ion implanted GaAs bipolar transistors

GaAs n-p-n bipolar transistors were fabricated by ion implanting Be and Se into bulk n-type substrate material. Devices with mesa collectors exhibit a d.c. current gain hFE ? 8 and a reverse bias leakage current of less than 10 nA.