Si-implanted GaAs Research Articles

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.

Structural modifications of silicon-implanted GaAs induced by the athermal annealing technique

We have used high-resolution X-ray diffraction and Raman spectroscopy to investigate structural modifications inside and outside the focal region of Si-implanted GaAs samples that have been irradiated at high power by a focused short-pulse laser. Si atoms implanted into the GaAs matrix generate exciton-induced local lattice expansion, resulting in a satellite on the lower-angle side of the Bragg peak. After the laser pulse irradiation, surface features inside and outside the focal spot suggest the presence of Bernard convection cells, indicating that a rapid melting and re-crystallization has taken place. Moreover, the laser irradiation induces a compressive strain inside the focal spot, since the satellite appears on the higher-angle side of the Bragg peak. The stress maximizes at the center of the focal spot and extends far outside the irradiated area (approximately 2.5-mm away from the bull’s eye), suggesting the propagation of a laser-induced mechanical wave. The maximum compressive stress inside the focal spot corresponds to 2.7 GPa. Raman spectra inside the focal spot resemble that of pristine GaAs, indicating that rapid melting has introduced significant heterogeneity, with zones of high and low Si concentration. X-ray measurements indicate that areas inside the focal spot and annealed areas outside of the focal spot contain overtones of a minor tetragonal distortion of the lattice, consistent with the observed relaxation of Raman selection rules when compared with the parent zinc-blende structure.

Athermal annealing of Si-implanted GaAs and InP

GaAs and InP crystals ion implanted with Si were athermally annealed by exposing each crystal at a spot of ∼2 mm diameter to a high-intensity 1.06 μm wavelength pulsed laser radiation with ∼4 J pulse energy for 35 ns in a vacuum chamber. As a result a crater is formed at the irradiated spot. The crater is surrounded by a dark-colored ring-shaped region which is annealed by mechanical energy generated by rapidly expanding hot plasma that formed on the exposed spot. The electrical characteristics of this annealed region are comparable to those of a halogen-lamp annealed sample. No redistribution of impurities due to transient diffusion is observed in the implant tail region. In x-ray diffraction measurements, a high angle side satellite peak due to lattice strain was observed in the crater and near crater regions of the athermally annealed sample in addition to the main Bragg peak that corresponds to the pristine sample. This high angle side satellite peak is not observed in regions away from the crater (⩾5 mm from the center of the crater in GaAs).

Activation of Si implanted in GaAs at high intensity As co-implantation

The electrical and structural properties of Si-implanted GaAs (with the ion energy of 100keV and the dose of 2×1013cm−2) after high intensity co-implantation of As ions (with the energy of 150keV, current density of 80μA/cm2 and implantation times up to 20s) and following furnace annealing have been investigated. Co-implantation of As ions in self-annealing regime (heating up to 700–800°C) forms the conductive layers with poor Si activation efficiency (<10%). RBS measurements showed the full recovery of crystalline structure of the implanted layers both with and without Si activation. The following furnace annealing (750°C for 20min) has increased Si activation efficiency up to 100%. The effect is supposed to be due to amorphization and following solid state epitaxial recrystallization of Si implanted layer in As excess conditions at elevated temperatures during As co-implantation.

Measurement of the damage profile of ion-implanted GaAs using an automated optical profiler

We describe an easy-to-use, computer-controlled optical method capable of determining the damage profiles in ion-implanted semiconductors. Using this method we measured the damage profiles in Si-implanted GaAs of various ion energies and ion doses. The resulting damage profiles are in good agreement with the total vacancy profiles generated by the transport of ions in matter (TRIM95), and the observed channelling effects not included in the TRIM calculations.

A study of the evolution of carrier and vacancy depth profiles with annealing temperature of Si-implanted GaAs

The activation of Si implanted into GaAs as a function of temperature and depth has been studied together with the distribution of implantation-induced vacancy defects by automated differential Hall measurement and positron annihilation spectroscopy respectively. A strong influence of implantation damage on the activation of the carriers has been observed, suggesting that two independent activation mechanisms are present dependent on the concentration of defects. An activation energy for the total sheet n-type carrier concentration of is measured while for the carriers in the first the activation energy is . The vacancy defects observed by positron annihilation measurements begin to anneal at temperatures below C; however, residual defects remain even after annealing at C. This study highlights the necessity to measure depth-resolved as opposed to depth-averaged data for the purposes of carrier activation modelling.

Simulation of uphill diffusion behaviour of Si-implanted GaAs

The anomalous `uphill' diffusion behaviour of implanted silicon in GaAs reported by Chen et al (1990 Jap. J. Appl. Phys. 29 L1950) has been simulated. From their experiment, this `uphill' diffusion was found to be implantation-dosage dependent. Below the threshold dosage of , no `uphill' diffusion was observed. In this work, we suggest that this anomalous behaviour is due to the formation of vacancy clusters when the implantation dosage is high enough. Silicon atoms are assumed to migrate through the Ga vacancies, which are comparatively mobile. On the other hand, the immobile clusters agglomerate silicon atoms around the vacancy peak, resulting in the `uphill' diffusion behaviour. A dip in carrier concentration profile also occurs at high dose implantations. Unlike the amphoteric nature on increasing silicon doping, the occurrence of this dip is attributed to the effect of the trapping of silicon atoms in the clusters where the former are not electrically activated.

GaAs implanted with silicon and carbon: electrical and optical characterization

Semi-insulating GaAs samples co-implanted with silicon and carbon have been studied by electrical and optical measurements in order to evaluate the compensation level obtained with different post-implant thermal treatments. A triple implant of silicon at different energies and doses has been performed so as to get a carrier concentration profile having a flat region. Carbon has been implanted at an energy so as to get the peak atomic concentration in the middle of the multiple silicon implant; four different carbon doses have been selected. Carbon has been confirmed to be an effective compensator of silicon, particularly if it is implanted in already activated Si-implanted GaAs: compensation efficiencies of the order of 60–70% are reached. The main feature of the photoluminescence spectra is an intense band whose intensity and peak energy depend on the implanted carbon dose. A simple relation between the peak energy of this band and the compensation is found which may provide a simple method to evaluate the compensation itself, once a calibration curve has been obtained from electrical measurements.

Optical measurement of the distribution of damage in ion-implanted GaAs

The distribution of damage in Si-implanted GaAs has been studied using differential reflectance (DR) spectroscopy. This novel and relatively simple optical technique has high sensitivity and allows the study of damage distribution in a dose range of 1*1011-3*1014 cm-2, which is difficult to access by other techniques. The effects of substrate temperature (30-300 degrees C) and crystal orientation ((100), (110) and (111) directions) on the damage profiles have also been measured. As expected, the overall damage was found to increase with increasing ion dose and to decrease with increasing temperature. The measured damage profiles, obtained by successively etching the sample and measuring the DR signal, have been compared with TRIM simulations. The magnitude and shape of the damage profiles were found to be very sensitive to crystal orientation.

Secondary electron emission from Si-implanted GaAs

The effect of the implanted Si into GaAs on the secondary electron yield was investigated using cross-sectional scanning electron microscopy. In the case of the isothermal annealing at 800 °C for 30 min, the yield was enhanced for the samples implanted at 150 keV with higher doses than 1×1014 cm−2 above which the activation efficiency of the implanted Si went down rapidly. The annealing temperature dependence also showed the enhancement of the yield for the samples with less activation efficiency. Hence, it was suggested that the yield was increased by the defects that reduced the activation efficiency.

Thermodynamic model for the annealing process of Si-implanted GaAs

The authors theoretically investigate the annealing process of Si-implanted GaAs. Four different annealing methods are considered, and the calculation of point defect concentrations is carried out, assuming that the conditions of the phase equilibrium for GaAs are different depending on the annealing method. In an anneal with As overpressure, GaAs is in equilibrium with a gas phase. When an SiO2 cap is used, GaAs will be in equilibrium with an As-rich liquid phase. In the case of an anneal with an Si3N4 cap, equilibrium with the outside phases is not established. Without any surface protection, GaAs is in equilibrium with a Ga-rich liquid. On the basis of the results, influences of the various annealing methods are discussed, and a new annealing method is proposed.

Annealing Behavior of HF-Treated GaAs Capped with SiO2 Films Prepared by 50-Hz Plasma-Assisted Chemical Vapor Deposition

Thermal stability of the SiO2/GaAs interface structures prepared by 50-Hz plasma-assisted chemical vapor deposition (PCVD) and the electrical activation of Si implanted into GaAs with SiO2 cap were investigated. X-ray photoelectron spectroscopy (XPS) analysis showed that the 50-Hz PCVD method at 200°C allowed the presence of an As-enriched layer, intentionally inserted by HF treatment before SiO2 deposition, at the SiO2/GaAs interface. After rapid thermal annealing (RTA) at 950°C for 20 s, in fact, the As-enriched layer still remained and it was effective in suppressing interfacial reactions which caused various shortcomings. In addition, carrier concentration profiles in excellent agreement with Lindhard-Scharff-Schiott (LSS) curves were reproducibly obtained by RTA in Si-implanted GaAs capped with both the As-enriched layer and the SiO2 film, demonstrating that this process is applicable to post-annealing of ion-implanted GaAs.

Si-implanted InGaP/GaAs metal-semiconductor field-effect transistors

A new device structure for Si-implanted GaAs metal-semiconductor field-effect transistors (MESFETs), with an InGaP thin film on the GaAs surface, is proposed. A 200 Å InGaP film passivated the GaAs surface and increased the Schottky barrier height on n-type GaAs layers with a carrier concentration as high as 3×1018/cm3 to more than 0.6 eV. These effects persisted after annealing at 800 °C for 10 min. The transconductance of 2-μm-gate MESFETs remained above 150 mS/mm at gate voltages up to 1.0 V. Si-implanted InGaP/GaAs MESFETs are thus promising devices for use in high-speed and low-noise integrated circuits.

Effect of Annealing Method on Vacancy-Type Defects in Si-Implanted GaAs Studied by a Slow Positron Beam

The effect of annealing encapsulants on the activation of Si implanted into GaAs was studied by slow positron beam annihilation. For encapsulants, two kinds of silicon nitrides and silicon dioxide were used and capless annealing under arsine ambient was performed for reference purposes. From the measurements of the Doppler-broadened profiles of the positron annihilation as a function of the incident positron energy, gallium vacancy concentrations were estimated. It was found that silicon dioxide cap annealing includes a high concentration of gallium vacancies, which is approximately 2.5 times larger than that for silicon nitride annealing and four times that for capless annealing. With the electrical measurement, the out-diffusion of Ga into the cap insulator film was found to have no enhancing effect on electrical activation.

The Study of Se- and Si-Implanted GaAs by Slow Positrons

The Study of Se- and Si-Implanted GaAs by Slow Positrons

The Study of Si, Se and O-Implanted GaAs by Slow Positrons

ABSTRACTVariable-energy (0–30keV) positron beam studies have been carried out on 200 keV Se-implanted and 70 keV Si-implanted GaAs specimens before and after annealing for electrical activation. From the measurements of Doppler broadened profiles as a function of incident positron energy, it was found that vacancy clusters with high concentration were introduced in the annealed specimen after Se implantation. From the parallel measurement of electrical characteristics, a higher activation efficiency was found for the higher concentration of vacancy clusters. That fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative. In contrast, no vacancy clusters were introduced in the Si-implanted GaAs. On the other hand, oxygen clustering was found in annealed specimen after O implantation.

Raman-scattering tomography studies on semiconductors

Distributions of phonons in ZnSxSe1-x, ZnTexSe1-x mixed crystals were observed by Raman-scattering tomography as stripes which were caused by the lack of some elements of the Raman tensor due to rotational twins around the (111) axis. The technique was also applied to the analysis of phonons on the surfaces of Si-doped GaAs crystals, Si-implanted GaAs crystals and epitaxial layers of ZnSe on GaAs crystals.

Drain Current DLTS Spectra and GaAs Substrate Crystal Effect on Low-Frequency-Oscillations of Si-Implanted Mesfets

ABSTRACTWe report drain-current (Id) deep level transient spectroscopy (DLTS) spectra and liquid-encapsulated-Czochralski-technique (LEC) GaAs crystal effect on low-frequency-oscillation (LFO) of wide gate (400-μm) Si-implanted GaAs metal- semiconductor field- effect- transistors (MESFETs). In the range of this experiment we could not find distinguishing DLTS peaks surely to be linked with Id-LFO of the MESFETs. Stoichiometric-melt growth LEC-boules showed relatively large Id-LFO phenomena. As-rich-melt growth LEC-boules showed tolerance to Id-LFO. We conclude that Id-LFO is not directly linked to deep centers themselves but interaction between deep centers and potential profiles and electrons. Stability of potential profile or band profile depends on “pinning’ center, which affects Fermi-level or quasi-Fermi-level stability. ‘Pinning’ center such as EL2s of ‘LEC GaAs crystals” is essential.

The effects of point defects on the electrical activation of Si-implanted GaAs during rapid thermal annealing

The effects of point defects on the electrical activation of Si-implanted GaAs during rapid thermal annealing were investigated using slow positron beam, cross-sectional transmission electron microscopy, and Hall measurements. The increase of the Ga vacancy concentration in the GaAs substrate induced by the SiO/sub 2/ cap layer on the substrate during annealing was observed to decrease the activation efficiency and the number of extrinsic stacking faults via the recombination of interstitials with vacancies. It was found that the efficiency of the carrier creation is not dependent upon the Ga vacancy concentration during the rapid thermal annealing of Si-implanted GaAs. Hence, it is proposed that the electrical activation of Si-implanted GaAs is not due to implantation-induced vacancies but to the self-exchange of interstitial Si atoms with the host Ga substitutional atoms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Si-implanted GaAs metal-semiconductor field-effect transistors with InGaP surface passivation film

The authors examine a novel device structure that contains an InGaP thin film on the GaAs surface. Since InGaP has a wider bandgap than GaAs, it is expected that phi /sub B/ (Schottky barrier height) would be increased by conduction band discontinuity in the InGaP/GaAs heterojunction and that the GaAs surface would be passivated. The dependence of the phi /sub B/ of Ti/Au contacts on the InGaP film thickness is measured using Si-doped GaAs layers with a carrier concentration as high as 3*10/sup 18//cm/sup 3/. Both enhancement- and depletion-mode Si-implanted MESFETs can be easily fabricated as planar devices in the same wafer by changing the ion implantation conditions. Si-implanted InGaP/GaAs MESFETs are thus promising devices for high-speed and high-density ICs with low-noise operation.