Radiation-thermal activation of silicon implanted in gallium arsenide

The layer density, density profile, and mobility of electrons in ²⁸Si-ion-doped layers of semiinsulating GaAs after radiation annealing with electron energy above and below the defect formation threshold and after thermal annealing in the temperature range T _a =590–830 °C are investigated. It is shown that for radiation annealing energy above the defect formation threshold ion-doped layers are formed with much lower annealing temperatures, and the degree of electrical activation of silicon in these layers is high and the density of electron mobility limiting defects is low. Fiz. Tekh. Poluprovodn. 33, 687–690 (June 1999)     

Tellurium implantation in GaAs

Electron concentration and mobility profiles for Te implanted semi-insulating GaAs samples annealed with a reactively sputtered silicon nitride protective layer (or cap) have been measured as a function of the dose of implanted Te and the annealing temperature. Results of high dose implants into n-type epitaxial samples are essentially the same as those obtained using semi-insulating material from different suppliers. Samples in which Ga was implanted either before or after the implantation of Te exhibited essentially the same electron concentration and mobility profiles as those in which only Te was implanted. Attempts to introduce As vacancies by preannealing Te implanted samples without a cap at temperatures between 550 and 700°C also had no effect on the measured profiles. The use of an aluminum oxy-nitride cap resulted in about twice the doping efficiency and three times the maximum electron concentration than was obtained with a silicon nitride cap for doses of 1 × 10¹⁴ Te ions/cm².     

A model for the formation of donor centers in silicon layers implanted with erbium and oxygen ions

Formation of donor centers in the course of annealing of layers of single-crystal silicon FZ-Si (grown by the float-zone method) and Cz-Si (grown by the Czochralski method) implanted with Er⁺ and O⁺ ions was simulated. The diffusion-kinetics equations accounting for the formation of erbium-related donor centers of three types were solved numerically. These centers were formed with the involvement of oxygen in the substrate or implanted oxygen and also self-interstitials I produced during annealing of implantation-induced defects; i.e., the Er-I, Er-O, and Er-O-I centers were considered. The results of calculations satisfactorily describe the concentration profiles of donor centers and also the influence of oxygen in the substrate and implanted oxygen on the dependence of the donor-activation coefficient of erbium on the annealing temperature in the range of 600–1200°C.     

Rapid thermal annealing of gallium arsenide implanted with sulfur ions

Sulfur ions were implanted into semi-insulating GaAs. A SiO₂ film was deposited by either of two methods onto the implanted surface. The samples were then subjected to either rapid thermal annealing (using halogen lamps) for 10–12 s at 805°C or to conventional thermal annealing for 30 min at 800°C. The content of GaAs components in the film was determined from the spectra of Rutherford backscattering. The electron-concentration profiles were plotted using the measurements of the capacitance-voltage characteristics. It is shown that sulfur diffuses in two directions, i.e., towards the surface and into the GaAs bulk. The former process is stimulated by vacancies formed near the semiconductor surface during the deposition of SiO₂. The coefficients of the “volume” diffusion of S and of the diffusion of S towards the surface are two orders of magnitude larger upon rapid thermal annealing than upon conventional thermal annealing, with the degree of S activation also being higher.     

Solid boron and antimony doping of Si and SiGe grown by gas source molecular beam epitaxy

Solid boron and antimony doping of silicon and SiGe grown by molecular beam epitaxy using disilane and germane as sources has been studied. Elemental boron is a well behaved p-type dopant. At effusion cell temperatures of 1700–1750°C, hole carrier concentrations in the 10²⁰ cm⁻³ range have been obtained. Elemental antimony doping shows surface segregation problems. For uniformly doped layers, the as-grown materials do not show n-type conductivity. Electron concentrations in the 10¹⁷ cm⁻³ range were obtained by post-growth conventional and rapid thermal annealing at 900 and 1000°C, respectively. The electron Hall mobility improves with optimum annealing time. Delta doping of buried layers exhibits slightly better incorporation behavior including significant surface riding effects.     

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.     

P-type doping of GaAs by carbon implantation

The electrical properties of C-implanted <100> GaAs have been studied following rapid thermal annealing at temperatures in the range from 750 to 950°C. This includes dopant profiling using differential Hall measurements. The maximum p-type activation efficiency was found to be a function of C-dose and annealing temperature, with the optimum annealing temperature varying from 900°C for C doses of 5 × 10¹³ cm⁻² to 800°C for doses ≥5 × 10¹⁴cm⁻². For low dose implants, the net p-type activation efficiency was as high as 75%; while for the highest dose implants, it dropped to as low as 0.5%. Moreover, for these high-dose samples, 5 × 10¹⁵ cm⁻², the activation efficiency was found to decrease with increasing annealing temperature, for temperatures above ∼800°C, and the net hole concentration fell below that of samples implanted to lower doses. This issue is discussed in terms of the amphoteric doping behavior of C in GaAs. Hole mobilities showed little dependence on annealing temperature but decreased with increasing implant dose, ranging from ∼100 cm²/V·s for low dose implants, to ∼65 cm²/V·s for high dose samples. These mobility values are the same or higher than those for Be-, Zn-, or Cd-implanted GaAs.     

Selenium implantation in GaAs

The dependence of carrier concentration and mobility profiles on the dose of 400 keV Se ions implanted into Cr-doped semi-insulating GaAs, and on the annealing temperature has been studied for doses ranging from 3 × 10¹²/cm² to 2 × 10¹⁵/cm² and for annealing temperatures between 800 and 1000°C. Sputtered aluminum oxy-nitride and silicon nitride films were used as encapsulants for protection of the implanted surface during annealing treatments. The carrier profiles exhibited deep tails for implantations along both random and {110} planar directions. It was found that annealing temperatures of 900°C or above were necessary to obtain high carrier density and mobility values for implantation doses above 1 × 10¹⁴/cm². Samples encapsulated with aluminum oxy-nitride films exhibited 3 to 4 times higher carrier concentration values and also slightly higher mobility values than those encapsulated with silicon nitride films. The maximum carrier concentration obtained was about 4 × 10¹⁸/cm³ with aluminum oxy-nitride films as the encapsulant.     

Preparation and properties of Mn-doped epitaxial gallium arsenide

The preparation of manganese-doped GaAs epitaxial layers growth from the liquid-phase, and Hall effect and resistivity measurements in the temperature range from 60 to 300°K, are described. An anomalous solubility of GaAs in the Ga + GaAs + Mn solution was observed and occurrence of a Mn₂As-phase in solution was identified. From the analysis of the Hall effect measurements the thermal activation energy of the manganese acceptor was determined. The energy decreases from 0·092 to 0·084 eV with the Mn-concentration in the epitaxial layers increasing from 6 × 10¹⁷ cm^?3 to 3 × 10¹⁹ cm^?3. The solubility of Mn in GaAs at the temperature of the preparation (850°C) was found to be about 4 × 10¹⁹ cm^?3.     

Spatial localization and diffusion of atomic silicon in delta-doped GaAs

Spatial localization and diffusion of atomic Si is studied inσ-doped GaAs by employing capacitance-voltage (CV) measurements and rapid thermal annealing. It is found that diffusion and segregation are irrelevant inσ-doped GaAs grown at temperatures below 550° C. Combination of rapid thermal annealing and capacitance-voltage profiling is a novel method which is most sensitive to diffusion and it is shown that this method is able to detect diffusion on a length scale of 10Å. CV-profile widths broaden from?40Å to 137Å upon rapid thermal annealing at 1000° C for 5 sec. The diffusion coefficient and the activation energy of atomic Si-diffusion in GaAs are determined to beD _o = 4 × 10^?4 cm²/s andE _a = 2.45 eV, respectively. The basic theory of CV-measurements on a quantum-mechanical electron system is developed.     

Low resistance bilayer Nd/Al ohmic contacts on n-type GaN

A bilayer Nd/Al metallization structure has been deposited onto low pressure organometallic vapor phase epitaxy grown n-type GaN ( 1 × 10¹⁸ cm⁻³) by electron-beam evaporation. Ohmic metal contacts were patterned photolithographically for standard transmission line measurement, and then thermally annealed at temperatures ranging from 200 to 350°C and from 500 to 650°C using conventional thermal annealing (CTA) and rapid thermal annealing (RTA), respectively. The lowest values for the specify contact resistivity of 9.8 × 10⁻⁶ Ω−cm² and 8 × 10⁻⁶ Ω−cm² were obtained using Nd/Al metallization with CTA of 250°C for 5 min and RTA of 600°C for 30 s. Examination of the surface morphology using atomic force microscopy as a function of annealing temperature revealed that the surface roughness was strongly influenced by conventional thermal annealing, it was smooth in the temperature range from 550 to 650°C for rapid thermal annealing. Auger electron spectroscopy depth profiling was employed to investigate the metallurgy and interdiffusion of contact formation.     

Characteristics of gallium arsenide structures and Gunn devices based on them fabricated using the radiation-thermal technology

Doped layers were produced by implanting sulphur ions into single-crystal GaAs and also into GaAs epitaxial films grown on semi-insulating substrates, with subsequent thermal annealing. An additional radiation treatment was performed using halogen lamps (photon annealing). Gunn devices and integrated circuits based on them were fabricated by planar technology. The additional treatment was shown to lead to an increase in the electron mobility in the layers due to the reduction of the concentration of scattering center. The Gunn-device structures, which were subjected to photon annealing, are characterized by better homogeneity and higher values of the current drop. Nearly ideal current pulses were generated in such structures, and no effects caused by trapping, as well as by the impact ionization, were observed.     

The effects of incomplete annealing on the temperature dependence of sheet resistance and gage factor in aluminum and phosphorus implanted silicon on sapphire

The temperature coefficient of resistivity (TCR) of ion implanted silicon can be significantly reduced by partially annealing the crystal damage produced during implantation. The extent to which this method can be used to temperature compensate the resistivity and the gage factor has been determined for 300 ohm-cm silicon on sapphire implanted with either 100 keV Al²⁷ or P³¹ ions. The implantations were made at room temperature parallel to the 〈100〉 axis and in four fluences ranging from 1 × 10¹³cm^?2 to 1·25 × 10¹⁵ cm^?2. Sheet resistance, Hall coefficient, and effective mobility were measured from ?150°C to 150°C for various anneal temperatures. It was possible to obtain very low temperature dependences of sheet resistance at 300°K for all dopant fluences by appropriate partial annealing. On samples having the lowest temperature dependence of sheet resistance, the gage factor was measured from ?75°C to 75°C. The measurements were made along the 〈100〉 direction for phosphorus doped samples, and along the 〈110〉 direction for aluminum doped samples for all four fluences. The gage factor and its temperature dependence for these crystal orientations are not drastically affected by the crystal damage. These results are interpreted in terms of a model previously developed to explain the effect of electron damage on the temperature dependence of the resistivity and the piezoresistance of silicon.     

Electric current controlled liquid phase epitaxy of GaAs on N+ and semi-insulating substrates

Electric current controlled liquid phase epitaxy (LPE) of GaAs has been performed on both n⁺ and semi-insulating substrates. Growth is induced by current flow across the substrate-melt interface. The furnace temperature is held constant during growth so that direct electrical control of the growth process is achieved. The dependence of the growth rate on both the electric current density across the substrate-melt interface and the ambient furnace temperature was determined. Current densities from 5 to 20 A/cm² were employed and furnace temperatures ranging from 680 to 800°C were used. Sustained steady state growth rates as small as 0.022μm/min and as large as 1.4μm/min were obtained. For a given furnace temperature and current density, the measured growth rates on semi-insulating substrates range from 48% to 77% of the rates obtained on n⁺ n substrates. The surface morphology of the epitaxial layers is observed to depend on the electric current density employed during growth. Electric current controlled doping modulation was studied in epitaxial layers grown from unintentionally doped melts. The degree of doping modulation achieved is approximately proportional to the change in applied current density. Approximately a 40% increase in the net electron concentration is obtained by changing the current density from 10 to 30 A/cm² during growth. Preliminary experiments with tin doped epitaxial layers indicate that similar changes in the amount of tin incorporation can be achieved.     

Electrical properties of Si:Er/Si layers grown by sublimation molecular-beam epitaxy

Temperature dependences of the concentration and electron Hall mobility in Si:Er/Sr epitaxial layers grown at T = 600°C and annealed at 700 or 900°C have been investigated. The layers were grown by sublimation molecular-beam epitaxy in vacuum (～10^?5 Pa). The energy levels of Er-related donor centers are located 0.21–0.27 eV below the bottom of the conduction band of Si. In the range 80–300 K, the electron Hall mobility in unannealed Si:Er epitaxial layers was lower than that in Czochralski-grown single crystals by a factor of 3–10. After annealing the layers, the fraction of electron scattering from Er donor centers significantly decreases.     

A high-temperature radiation-resistant rectifier based on p<Superscript>+</Superscript>-n junctions in 4H-SiC ion-implanted with aluminum

A combination of a high-dose (5 s- 10¹⁶ cm^-2) implantation of Al ions into epitaxial n-type 4H SiC layers grown by chemical deposition from th e vapor phase and rapid (15 s) thermal annealing at 1700–1750°C has been used to form layers with a rectangular impurity profile according to the mechanism of solid-phase epitaxial crystallization. The combined effects of enhanced diffusion of radiation defects after implantation and gettering of defects during annealing bring about an improvement in the quality of the initial material, which ensures an increase in the diffusion length of the minority charge carriers by several times. Metastable states annealed within different temperature ranges are formed in SiC under the effect of irradiation with various particles. Low-temperature annealing of radiation defects increases the radiation and temporal lifetime of devices under irradiation. High-temperature annealing of radiation defects makes it possible to vary the lifetime of nonequilibrium charge carriers, i.e, vary the frequency range of devices. The radiation resistance of SiC-based devices increases as the operation temperature is increased to 500°C.     

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.     

Some characteristics of highly N-doped VPE grown GaAs epilayers

The doping behaviour of S and Se in the VPE growth of GaAs at 760 and 660°C is studied by carrier concentra-tion, mobility, photo and cathodoluminescence measure-ments. The carrier concentration increases linearly with the partial pressure of S or H₂Se up to a solubi-lity limit, the highest value of which is obtained with Se at about 10¹⁹cm^-3. The mobility for Se-doped layers is higher than for S-doped ones when n > 4.10¹⁷cm^-3, and a mobility decrease is observed for both at dopings exceeding the solubility limit. Postgrowth annealing at the growth temperature of highly doped samples decreases their carrier concentration to values corresponding to the bulk solubility limit. The decrease of the room temperature luminescence intensity at high doping levels in tentatively interpreted as due to precipitate for-mation. Finally, the linear dependence on the dopant partial pressure of the impurity incorporation as well as the observed annealing behaviour are interpreted by an incorporation mechanism controlled by the surface states.     

Activation and distribution of silicon implanted in gallium arsenide as a result of isothermal radiation annealing

The method of capacitance-voltage characteristics is used to investigate the concentration profiles n(x) of ²⁸Si, implanted in GaAs [E=50 and 75 keV, F=(1.88–6.25)×10¹² cm⁻²] after “photonic” and “electronic” annealing with a protective dielectric coating covering the surface and without it. It is shown that in contrast to thermal annealing (800 °C, 30 min), after photonic and electronic annealing diffusive redistribution of silicon into the interior of the GaAs sample is observed. The diffusion coefficient D and degree of activation η increase as the temperature is increased in the case of photonic annealing and as the power is increased in the case of electronic annealing. The values of the activation energy of the processes for D and η for radiation annealing (photonic and electron) are lower than the corresponding values for thermal annealing. The values of D and η after photonic and electronic annealing without the protective dielectric coating are higher than with it. Fiz. Tekh. Poluprovodn. 32, 1153–1157 (October 1998)     

The annealing of 1 MeV implantations of boron in silicon

Buried layers of boron in silicon have been made by 1 MeV implantations up to a dose of 10¹³ cm^?2. The annealing of the implantation damage has been studied with Van der Pauw and Hall measurements. It is concluded that lattice damage reduces the mobility only for annealing temperatures below 600°C. The average mobilities measured after annealing at temperatures above 600°C correspond accurately to the values calculated from the most recent literature data, based on scattering by the lattice and by the active impurities. Complete activation was obtained after 60 min annealing at 700°C.