Undoped Semi-insulating GaAs Research Articles

Investigation of changes of As precipitates in semi-insulating GaAs crystals at several temperatures by infrared light scattering tomography

Thermal behavior of arsenic precipitates in undoped semi-insulating GaAs crystals has been investigated. Crystals heat-treated at a temperature between 500 and 1150°C were observed by infrared light scattering tomography, which is powerful technique capable of detecting the arsenic precipitates. The arsenic particles on the dislocations became large increased in scattering intensity with temperatures from 800 to 1000°C. A dramatic change occurred above 1100°C: the images disappeared over the whole area. This disappearance means that the arsenic precipitates dissolves into the GaAs crystal. Using the samples in which the excess arsenic was solid-soluted, the same experiments were repeated. At 800–1000°C, the scattering images of the dislocations again appeared. Below 600°C, new images, consisting of misty zones of scattering, were observed in the dislocation-free areas. This suggests that the excess arsenic condenses like mist over the limit of saturation solubility.

Band-edge photorefractive effect in semiconductors

We report here for the first time, two-beam coupling energy transfer using the Franz–Keldysh electrorefractive effect in photorefractive semiconductors. A large beam coupling gain coefficient (Γ=2.8 cm−1) exceeding the absorption coefficient (α=2.0 cm−1) is obtained in undoped semi-insulating GaAs using the new photorefractive process. The new photorefractive process differs from conventional photorefractivity in that the direction of energy transfer is dictated by the direction of an externally applied electric field. Using a moving grating technique and combining the electrorefractive grating with the conventional electro-optic grating, a very large gain Γ=16.3 cm−1 (α=3 cm−1, crystal length l=4mm) resulting in net amplification by more than a factor of 200 has been demonstrated.

Properties of semi-insulating GaAs grown by a vertical molten zone method

Electrical and optical measurements are reported for samples from two undoped semi-insulating GaAs crystals grown by a vertical molten zone method. The electrical data, taken over the range 290–420 K, included results for samples from both crystals that were so close to intrinsic as to require an ambipolar correction in determining the electron concentration. The compensation balance in this material is controlled by the EL2 midgap defect, of which the fraction ionized depends on trace presence of CAs shallow acceptors, and of shallow donors, probably including SiGa . An increase of the latter towards the tail (top) end of one crystal led to a reduction of the EL2 ionized fraction, and a lowered resistivity—but one still within the conventional semi-insulating range. Carbon was measured from the strength of its local vibrational mode absorption, while near-infrared measurements showed that EL2 was present in a concentration ∼1016 cm−3, with relatively small variation across a wafer.

Ion Implantation in InSb Grown on GaAs

ABSTRACTBe, S, Si, and Ne implantations were performed at room temperature into InSb layers grown on undoped semi-insulating GaAs substrates. The implant damage in InSb is of ntype behavior. The implanted material was subjected to both isochronal and isothermal annealing schemes using a molybdenum strip heater. A maximum p-type activation of 90 % and si-type activation of 16 % was achieved for Be and S implants, respectively. Si implant has an amphoteric doping behavior.

Undoped semi‐insulating GaAs crystals grown by a modified low pressure LEC method

AbstractA modified low pressure in‐situ synthesis LEC method of growing undoped SI (semi‐insulating) GaAs crystals has been established. The key points for controlling melt composition and As evaporation during synthesis and growth have been described. Using this novel approach, crystals are able to be grown from the nominal melt composition in the range of 0.491–0.499 As fraction with high reproducibility. Some characteristics of the undoped SI crystals grown by the present work including electrical properties, dislocation density, carbon and EL2 concentrations and thermal annealing effects have been studied.

Activation uniformity improvement of undoped semi-insulating GaAs with an improved post-implant anneal furnace

In this article we illustrate how by suitable furnace design, the radial thermal gradients generated on a GaAs substrate during the post-implant anneal cycle can be virtually eliminated, and how such a technique can result in appreciable improvements in on-wafer activation uniformity with improved activation efficiency uniformity in going from the seed to the tail-end wafer of an ingot.

Activation analysis of rapid thermally annealed Si and Mg implanted semi-insulating GaAs

Electronic properties of Si and Mg implants in undoped semi-insulating GaAs are studied. The activation of the implants is achieved by rapid thermal annealing. The effects of implantation dose and anneal temperature on the measured electrical activity are investigated. In spite of similar depth distributions and implantation damage characteristics, a marked difference between the activations of the Si and the Mg ions is observed for the dose range considered (3×10^12 – 1×10^14 cm^–2). Lattice strain measurements performed by x-ray rocking curves indicate that the residual implantation damage after annealing is not largely responsible for this difference. The difference is mostly electronic in character, as also suggested by photoluminescence measurements. At high annealing temperatures, changes in the compensating properties of undoped semi-insulating GaAs are suspected, and are found to play an important role in the activation of implanted ions, affecting the n- and p-type dopants conversely.

Temperature Dependence of Photocurrent in Undoped Semi-Insulating Gallium Arsenide

The temperature dependence of extrinsic and intrinsic photocurrent, in undoped semi-insulating GaAs containing EL2, in the range 20 K to 200 K is studied. The photocurrent increases ecponentially as the temperature is decreased down to 50 K and then decreases slightly for lower temperatures. It is argued that the exponential increase in photocurrent is due to the thermal activation energy of hole capture cross-section of the lifetime controlling centre

Spatial distribution of residual shallow acceptors in undoped semi-insulating GaAs

The spatial distribution of residual shallow acceptors in undoped semi-insulating GaAs has been studied quantitatively by electronic Raman scattering with a spatial resolution of ∼50 μm. This acceptor distribution has been correlated with the spatial distribution of the compensating EL2 donor in its neutral charge state measured by near-IR absorption topography. An enhanced acceptor concentration is found in regions which show high-IR absorption: From the comparison with low-temperature cathodoluminescence results, it is found that the intensity of the band-to-acceptor recombination normalized to the band-to-band luminescence intensity reproduces the acceptor distribution measured by Raman scattering. Implications of the present result on the compensation model for undoped semi-insulating GaAs are discussed.

A bipolar mechanism for alpha-particle-induced soft errors in GaAs integrated circuits

The alpha-particle-induced collected charge in undoped LEC semi-insulating GaAs is measured in n/sup +/-i-n/sup +/ and n/sup +/-p-n/sup +/ isolation structures and is compared with the results of an analytical model based on a bipolar mechanism. In n/sup +/-i-n/sup +/ isolation structures, a collected-storage multiplication phenomenon induced by alpha-particle incidence is observed. The measured collected charge is about three times the alpha-particle-generated charge. This phenomenon can be attributed to charge transfer between two adjacent n/sup +/ regions. The dominant charge-collection process continues for 2.4 ns in n/sup +/-i-n/sup +/ isolation structures, but in n/sup +/-p-n/sup +/ isolation structures, it stops within 0.8 ns. The measured collected charge decreases as the isolation gap and background acceptor concentration increase. These experimental results can be explained semiquantitatively by the analytical model. This suggests that the primary mechanism of soft errors in GaAs ICs is a bipolar mechanism.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Non-alloyed ohmic contacts on rapid thermally Zn diffused GaAs

Rapid thermal diffusion of zinc into undoped semi-insulating GaAs substrates from spin-on zinc silica film is performed in A.G. Associates Heat pulse 410 system with tungsten-halogen lamps as the heat source. The Zn diffused layers were electrically characterised by Van der Pauw measurements and showed the formation of p + layer. The surface morphology of the diffused layers were observed by optical microscope and scanning electron microscope. The depth profiling of diffused layers by secondary ion microscopy showed considerable diffusion of Si along with Zn. Radio frequency sputter depositing Si 3N 4 was found to be a good diffusion barrier for Zn diffussion. Non-alloyed ohmic contact with low contact resistivity was implemented on these Zn diffused layers.

Electron-beam doping of Si into GaAs: The annealing behaviour of photoluminescence

Si impurities are introduced in (100)-oriented undoped semi-insulating GaAs at 50°C by using an electron-beam doping method from a Si impurity sheet, which is in contact with a GaAs surface. The Si surface is irradiated with a fluence of ∼ 5 × 10 17 electrons cm −2 at 7 MeV. Before and after annealing at 300°C for 20 min with a SiO 2-cap layer, the photoluminescence spectra at 77 K indicate two dominant peaks which are probably attributed to silicon acceptors, Si As, at 1.48 eV and gallium antisite defects, Ga As, at 1.445 eV. When the annealing temperature is higher than 600°C, the band-gap transition spectra appear at 1.51 eV. The hole concentration for a sample annealed at 700°C is measured to be 1–4 × 10 16 cm −3 with a nearly constant depth distribution in the range of 0.5–5 μm.

Electron beam doping of Si into GaAs in the overlayer Si/substrate GaAs and the sandwiched system of GaAs/Si/GaAs

Si atoms were introduced in (100)-oriented undoped semi-insulating GaAs at 50 ° C by using an electron-beam doping method from a Si sheet. A Si sheet with a thickness t of ∼ 0.5 mm was sandwiched between two wafers of GaAs: GaAs (layer 3)/Si (layer 2)/GaAs (layer 1) (sandwiched array). The surface of layer 3 was irradiated with a fluence of 5 × 10 17 electrons cm −2 at 7 MeV. After annealing at 800 ° C for 20 min with a SiO 2 cap, the 0.6 mm thick GaAs wafers (the layers 1 and 3) converted to p-type, and the peak carrier concentrations at the surfaces of layers 1 and 3, which were in contact with the Si surface, were ∼ 3X10 17 and ∼ 4x10 17 cm −3, respectively. The photoluminescence spectra at 77 K for layers 1 and 3 indicated two dominant peaks, which were attributed to the Si acceptor, Si As,, at 1.48 eV and to the band gap transition at 1-51 eV. In the case of the sandwiched array electron-beam doping was experimentally determined to be more effective than in the case of the two layer array (an overlayer Si/substrate GaAs).

Determination of the FR3 Acceptor Level by Direct Excitation of the FR3 EPR in Undoped Semiinsulating GaAs

Determination of the FR3 Acceptor Level by Direct Excitation of the FR3 EPR in Undoped Semiinsulating GaAs

Influence of boron related defects on activation of silicon implanted into undoped semi-insulating GaAs: Fumio Orito et al, J appl Phys, 63, 1988, 2691–2693

Influence of boron related defects on activation of silicon implanted into undoped semi-insulating GaAs: Fumio Orito et al, J appl Phys, 63, 1988, 2691–2693

SELF-TRANSMISSION OF PICOSECOND LIGHT PULSES IN GaAs

In this paper, we report the experimental and theorical results of self-transmission of pi-cosecond light pulses of 1 μm in undoped semi-insulating GaAs at Brewster angle incidence. The best fitting density of the deep level EL2 is 1.2×l016cm-3, the two-photon absorption coefficient is 29 cm/GW and the free-carrier cross section is 2.7×10-17 cm2.

Characterization of Deep-Level Defects in Semi-Insulating GaAs and InP by Photoinduced Transient Spectroscopy (PITS)

AbstractDeep states in semi-insulating (SI) materials :GaAs:Cr ,un-doped GaAs and InP:Fe are investigated by Photoinduced Transient Spectroscopy (PITS) .The relationship between the Hall mobility in undoped SI GaAs and occurrence of the EL2-related peak in the PITS spectrum is shown.

Defect Formation During Zn Diffusion into GaAs

AbstractThe microstructure induced by the Zn diffusion at 1170 K into doped and undoped semi-insulating GaAs single crystals was characterized for various diffusion times t &lt; 1740 min by analytical electron microscopy. The results were compared with Zn concentration profiles obtained by spreading resistance measurements (SRM) on the same samples. At the diffusion front the formation of prismatic interstitial dislocation loops, dislocation networks, and of cavities partly filled with Ga was observed. Closer to the surface facetted voids and, for the undoped samples, vacancy-type dislocation loops formed. The near surface region of highest Zn-concentration showed a high density of Zn-rich precipitates. A model is presented which accounts .for these observations. It is based on fast interstitial Zn diffusion and the kick-out mechanism for interstitial-substituional exchange.

Characterization of residual carbon in semi-insulating GaAs

We have found that undoped semi-insulating GaAs substrates convert from semi-insulating to strongly conducting p-type behavior following high-temperature annealing (830 and 885 °C) for long periods of time (22–60 h). Remarkably similar results have been obtained for both liquid-encapsulated Czochralski and horizontal Bridgman undoped semi-insulating GaAs synthesized by various manufacturers. Hole concentrations measured at room temperature are about p=9.1×1015 and 3.6×1016 cm−3 after 830 and 885 °C anneals, and p is uniform throughout the 380 to 510 μm substrate thickness for 885 °C anneals. Hall-effect measurements of carrier freeze-out indicate that residual carbon acceptors are the dominant shallow-acceptor species. Conversion to p type appears to arise from out-diffusion of EL2 deep donors and from formation of an additional acceptor-type native defect which also results from arsenic out-diffusion during annealing.

Undoped Semi-Insulating GaAs of Very Low Residual Acceptor Concentration

We have studied undoped GaAs of shallow acceptor concentrations close to and below 5·1014cm-3. After ingot annealing with slow cooling rate this material shows resistivity values below 107 Ωcm, spanning several orders of magnitude. By an additional annealing procedure these values can be raised to some 107 Ωcm. DLTS results are presented indicating that the electrical characteristics in the ingot annealed state are governed by uncompensated deep donors shallower than EL2, mainly EL6 near Ec -0.35 eV. After the additional annealing a drastic decrease in EL6 concentration is observed, which explains the rise in resistivity. This is confirmed by theoretical calculation of the resistivity in dependence of the EL2 and EL6 to net acceptor compensation ratio, which agrees quantitatively with the experimental values.