Electrical profiles from zinc implanted GaAs

Hole concentration and mobility profiles have been measured for 1015Zn+/cm2 implanted into GaAs at room temperature. After annealing at 800°C the peak hole concentration for a 60 keV implant was in excess of 1019 holes/cm3 and decreased with increasing energy up to 450 KeV.     

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.     

Selective carrier removal using oxygen implantation in GaAs

It has been reported that free-carrier compensation can be achieved using oxygen implantation and can remain stable even after annealing at temperatures up to 900°C. It is demonstrated that carrier removal rate is drastically dependent on the initial donor species. It is very likely that carrier removal in Si-doped layers takes place via formation of Si-O complexes.     

Carrier compensation in O+ implanted n-type GaAs

Results of electrical measurements on 1 MeV O⁺ implanted n-type GaAs are reported. After annealing the implanted material it is found that the free carrier compenasation rate (k), defined by Favennec[1] as the number of carriers removed per oxygen atom, can be dependent upon both the starting material and the implanted dose.     

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.     

The effect of boron,oxygen, and fluorine in ion implanted GaAs

Effects of boron, fluorine, and oxygen in GaAs have been investigated by electrical characterization using current-voltage, capacitance-voltage and deep level transient spectroscopy techniques. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². Carrier compensation was observed in each implanted sample. The compensation effect strongly depended on ion implantation condition and ion species. More free carriers were compensated for higher dose and heavier species; however, severe surface damage would also be induced that degrade electrical performance. Rapid thermal annealing treatment showed the heavier ion implanted samples to be more thermally stable. Defect levels for each implanted species were compared and identified. A native shallow defect E4 was easily removed by ion implantation. In higher dose and heavier ion implantation, both electron and hole traps were induced. However, in some cases, heavier ion implantation also removed native defects. Acceptor-type surface states were created by implantation that degrade material electrical characteristics and also reduce the effect of compensation. The damage induced traps were mostly point-defects or point-defect/impurity complexes as evidenced by sensitivity to heat treatment.     

Comparison of doping profiles in capless annealed and dielectrically capped — Annealed ion implanted GaAs

Recent results of a capless method of annealing ion implanted GaAs are reported. The physical mechanism and effectiveness of the process are described and comparison of doping profiles from wafers annealed with a reactively sputtered Si₃N₄ dielectric encapsulation and with the capless process is given. Capless annealing is shown to consistently result in narrower profiles for various dopants and implant energies. The observed differences are shown to be consistent with enhanced diffusion in the dielectric capped samples, and the effective diffusion coefficients, which are of the order of 10^?15 cm²/s for Se, differ by as much as a factor of two.     

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.     

Photoluminescence of Be implanted Si-doped GaAs

Degenerately doped n-type GaAs produces band-to-band luminescence with the peak energy dependent on the carrier concentration. In this study the photoluminescence of Si-doped GaAs is examined after implantation with high energy Be ions and annealing. The band-to-band peak energy in the unimplanted (reference) material is shown to be smaller than reported values in Te-doped GaAs of the same carrier concentration. This is attributed to compensation in the Si doped material as a result of its amphoteric nature. For the implanted samples, no luminescence was recorded for the unannealed samples or those annealed at 400°C and 500°C. Comparing the relative peak intensities from material annealed at 600°C for 15 min and 30 min indicates an increase in the number of As vacancies with anneal time. For samples annealed at 700°C and 800°C, the dominant luminescence is associated with Ga_As antisite defects. It is suggested that formation of these defects occurs predominantly only at these higher temperatures. Crystal recovery as measured by the luminescence intensity increased with both anneal temperature and time. For the implanted sample annealed at 800°C for 15 min, the dominant peak height was 25% of that from the reference sample.     

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.     

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.     

Silicon implanted super low-noise GaAs MESFET

Super low-nose GaAs MESFETs have been fabricated using direct ion implantation into undoped LEC substrates. Microwave results at 12 GHz include a noise figure of 1.3 dB, with an associated gain of 10.3 dB and a maximum available gain of 14.9 dB.     

Carrier removal after H1+, H2+ or H3+ implants into GaAs

It is demonstrated that the carrier removal caused by implanting equivalent doses of H1+ H2+ and H3+ ions into GaAs is identical and approximately independent of the ion energy in the range 300?500 keV. Some recovery of carriers removed occurs at about 250°C.     

GaAs载流子的超快动力学特性

利用飞秒瞬态反射谱,研究了GaAs的载流子的超快动力学特性。根据实验结果,分析了弛豫过程,并通过计算,分析了自由载流子和晶格温度效应对弛预过程的影响,并给出了定量计算结果,分别为-7.33x10~(-4),0.85×10~(-4)。     

Incoherent annealing of implanted layers in GaAs

Incoherent light from filament lamps focused by elliptical mirrors has been used to activate implanted layers in GaAs. 4 × 10¹⁴Si⁺cm^-2and 2 × 10¹⁴Zn⁺cm^-2implants were annealed with Si3N4deposited by CVD at 400°C providing a surface protective layer. By taking advantage of the focusing properties of elliptical mirrors, most of the emitted light could be concentrated onto the GaAs to give annealing times × 1 sec. Differential Hall measurements show peak carrier concentrations of 6.5 × 10¹⁸cm^-3and 50% activation for the n+ layers. The Zn implants were completely activated and doped to ∼ 2 × 10¹⁹cm^-3. These results, together with the short annealing times, suggest the present approach to be an attractive alternative to both laser and conventional thermal annealing.     

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.     

The electrical properties of zinc implanted GaAs

The electrical properties of zinc implanted GaAs have been measured as a function of ion dose, ion energy, implant temperature and annealing temperature and time using either evaporated aluminium layers or pyrolytically deposited Si₃N₄ as the encapsulant during annealing. The electrical profiles depend on all the above variables and thus profiles can be tailored by varying the relative magnitudes of these parameters. It is important to note that hole concentrations in excess of 1 × 10¹⁹ cm^?3 can be obtained following an anneal at temperatures as low as 650°C. Also, at the same annealing temperature, profile depths can be varied from 0.2 to about 1 μm by correct choice of implantation parameters. Aluminium coatings are acceptable for annealing temperatures up to 700°C but Si₃N₄ is required at higher temperatures.     

Threshold voltage of ion implanted GaAs MESFET

Threshold voltages for ion implanted GaAs MESFETs are measured and shown to have good coincidence with calculated results. The effect of implantation energy on threshold voltage is discussed. The optimum implantation energy is about 45 ~ 60 keV.     

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.