Martin Parenteau

Electron and neutron radiation-induced order effect in gallium arsenide

Electron (7 MeV) and neutron (1 MeV equivalent fluence damage in silicon) radiation effects in GaAs grown by the metallorganic chemical vapor deposition method are investigated. One series of samples was intentionally undoped, and another was doped n-type to 2.5*10/sup 15/ Si/cm/sup 3/. The fluences ranged from 10/sup 10/ to 6*10/sup 15/ cm/sup -2/ for electron irradiation and from 10/sup 12/ to 3*10/sup 15/ cm/sup -2/ for fission spectrum neutron irradiation expressed as 1 MeV equivalent fluence in silicon. The radiation damage was characterized by low-temperature photoluminescence (PL) measurements using 1.58 eV laser excitation, deep level transient spectroscopy and transport measurements. The observed decrease of trap concentration accompanied with an increase in PL intensity at lower fluences, an increase in the density of traps at higher fluences, and a fluence-dependent oscillatory PL intensity for acceptor levels indicate radiation-induced order at low fluences following by nonuniform reorganization of defects with radiation in GaAs. >

A mobility study of the radiation induced order effect in gallium arsenide

N-type gallium arsenide doped with silicon was irradiated with reactor neutrons to 10/sup 12/, 3/spl times/10/sup 12/, 10/sup 13/, 3/spl times/10/sup 13/, 10/sup 14/, 3/spl times/10/sup 14/, 10/sup 15/, and 3/spl times/10/sup 15/ cm/sup -2/ (1 MeV equivalent fluence). The temperature dependence of the mobility was obtained after irradiation and annealing to 550/spl deg/C for 30 minutes. The maximum value of the mobility, /spl mu//sub max/, with respect to temperature was obtained as a function of fluence. For samples which have been irradiated and then annealed, /spl mu//sub max/ goes through a maximum at a fluence of 10/sup 13/ cm/sup -2/ and is 10% higher than in the unirradiated samples. At higher fluences, the mobility degrades. We attribute the increase in mobility at lower fluences to a radiation induced order effect. The disappearance of the deep level EL12 could be associated with this effect. At higher fluences where the mobility degrades, we observe by photoluminescence spectroscopy, the gallium vacancy, a point defect introduced by the irradiation, and the transfer of the silicon atom from the gallium site to the arsenic site. This suggests that growth of the gallium vacancy or the silicon at the arsenic site can be associated with mobility degradation. >

Radiation induced carrier enhancement and intrinsic defect transformation in n‐GaAs

Gallium arsenide grown by the metallorganic chemical vapor deposition method and n doped with silicon to a concentration of 1015 cm−3 was exposed to reactor neutron irradiation in the 1012 to 3×1014 cm−2 1 MeV equivalent fluence range. Studies of the defects through deep level transient spectroscopy (DLTS), photoluminescence (PL), and transport measurements on this material indicate correlation between the nature and density of defects, and some of the transport parameters. Contrary to the general perception of degradation of electronic properties of semiconductors on nuclear irradiation, we observe enhancement in some of the electrical/optical properties of GaAs on irradiation at lower fluence levels. These properties degrade on irradiation at higher fluences. The PL intensity of irradiated GaAs increases over the 1×1012 to 1×1013 cm−2 fluence range. At 1×1013 cm−2, the increase in the signal from different PL peaks ranges from 25% to 200%. Similarly, the carrier density of irradiated GaAs, as determined...

Particle dependence of the gallium vacancy production in irradiated n-type gallium arsenide

The relative introduction rate of the gallium vacancy in n-type GaAs irradiated with /sup 60/Co /spl gamma/ rays, 7 MeV electrons, fusion (14 MeV) and fission (1 MeV) neutrons, protons (0.6 to 200 MeV), deuterons (1 to 10 MeV), /spl alpha/ particles (2.5 to 10 MeV), lithium (5 to 20 MeV) and oxygen ions (10 to 30 MeV) has been determined. Effects of annealing are reported. The measured introduction rates obtained with proton irradiation for energies up to 10 MeV, and for the heavy ions agree reasonably well with Rutherford scattering, NIEL calculations and the TRIM simulation. The results for electron irradiation also agree with the corresponding NIEL calculations.

Damage coefficient associated with free exciton lifetime in GaAs irradiated with neutrons and electrons

The lifetime τ of the free exciton at T=17 K in irradiated GaAs has been determined by the reflectance of layers grown by metalorganic chemical vapor deposition and of semi‐insulating samples grown by the liquid‐encapsulated Czochralski method. The samples had been irradiated with 1 MeV and thermal neutrons, and with 7 MeV and white electrons up to 7 MeV. The linear increase of τ −1 as a function of the fluence is explained by a simple kinetics model, which applies especially well to the epitaxial layers. The damage coefficient kτ associated with this lifetime has been measured. For the defects created by all types of radiation, the radius associated with the cross section for the capture of excitons is three to ten times the radius of the free exciton. The exciton transition energy is found to decrease as its reflectance structure is broadened.

FORMATION OF EL2, ASGA AND U BAND IN IRRADIATED GAAS : EFFECTS OF ANNEALING

Gallium arsenide (GaAs) which was grown by metallorganic chemical vapor deposition, doped n with silicon to 2×1015 cm−3, and irradiated at room temperature with 1 MeV neutrons in the fluence range 1012 cm−2 to 3×1015 cm−2, has been studied by deep level transient spectroscopy (DLTS) and by far infrared photoluminescence (PL) spectroscopy. We report the effect of annealing at 550 °C for 30 min, which, in irradiated GaAs, is to introduce the gallium vacancy (VGa). The DLTS signal at 780±40 meV, attributed to the EL2 deep level, has an introduction rate of about 3×10−2 cm−1 in the unannealed case, and 0.19±0.02 cm−1 in the annealed case. The PL signal at 702 meV has been attributed to a phonon‐assisted transition of the EL2 defect, a defect which has been identified as the isolated arsenic antisite (AsGa+). The PL peak increases in intensity up to fluences of 3×1013 cm−2, before decreasing at higher fluences. After annealing, its intensity increases up to fluences of 1015 cm−2, before decreasing at the highe...

Time-resolved spectroscopy of irradiated n-GaAs

Gallium arsenide films were grown by the metallorganic chemical vapour deposition method and doped n-type with silicon to concentrations of 2/spl times/10/sup 15/ and 2/spl times/10/sup 16/ cm/sup -3/. The lifetime (/spl tau/) of the band-to-band recombination process was measured at 77 K using an optical time-resolved spectroscopy technique. The pre-irradiated values ranged from 350 to 550 ps. The samples were irradiated at room temperature with /sup 60/Co gamma rays, fission neutrons, 7 MeV electrons, protons (0.6 to 500 MeV), alpha particles, and lithium and oxygen ions. Degradation constants (K/sub /spl tau//) attributed to non-radiative processes generated by radiation-induced defects are reported. K/sub /spl tau// is compared to the previously published degradation constants associated with the photoluminescence intensity (K/sub PL/) in the continuous mode, and to the previously published introduction rate (b) of the silicon defect at the arsenic site (Si/sub As/) K/sub /spl tau//, K/sub PL/ and b(Si/sub As/) are compared to non-ionizing energy loss calculations and to the Rutherford scattering theory of the cross-section.

Gigaelectron-volt heavy ion irradiation of gallium arsenide

Gallium arsenide grown by metalorganic chemical vapor deposition and n doped with silicon to nominal concentrations of 2×1015, 8×1015, and 2×1016 cm−3, was irradiated with 1.04 GeV bromine ions at a fluence of 5×109 cm−2, 1.7 GeV iodine ions at a fluence of 2.7×109 cm−2, and 1.5 GeV gold ions in the fluence range of 1.0×106–2.2×109 cm−2. The effects were analyzed by photoluminescence (PL) spectroscopy. The donor-to-gallium vacancy (D-VGa) and the donor-to-silicon-acceptor (D-SiAs) transitions are observed in the PL spectra of the irradiated samples. The former occurs at 1.476 eV, and the latter at 1.483 eV when the recording temperature is 6.5 K. The relative introduction rates of the VGa and SiAs defects for these ions are compared to those obtained in previous studies where electrons, protons, alpha particles, lithium ions, and oxygen ions were the irradiating particles. The measured values correlate with relativistic (Darwin–Rutherford) or nonrelativistic (Rutherford) scattering theory, depending on th...

Photoluminescence study of gallium vacancy defects in gallium arsenide irradiated by relativistic protons

Epitaxially grown n-type gallium arsenide films, doped with silicon to concentrations of 2/spl times/10/sup 15/ and 2/spl times/10/sup 16/ cm/sup -3/ were exposed at room temperature to 200, 350, and 500 MeV proton irradiation at fluences of 3/spl times/10/sup 11/, 10/sup 12/, 10/sup 13/, 3/spl times/10/sup 13/ 10/sup 14/ and 10/sup 15/ cm/sup -2/. The effects of the irradiation were determined through low temperature continuous photoluminescence spectroscopy. Two radiation-induced donor-to-acceptor transitions were observed. The one at 1.476 eV has been associated to the gallium vacancy acceptor (V/sub Ga/) and the other at 1.482 eV to the silicon at the arsenic site acceptor (Si/sub As/). The relative introduction rate of these two defects has been measured in the irradiated samples before and after annealing at 550/spl deg/C for 30 minutes. The introduction rates are higher than those predicted by relativistic elastic scattering cross-section theory in the energy range studied here. We conclude that inelastic scattering contributes to the cross-section. The introduction rates are lower than non-ionizing energy loss (NIEL) calculations in the 200 to 500 MeV energy range. We suggest that the proton inelastic scattering parameter used in NIEL needs revision. The relativistic inelastic scattering formula is closer to experiment than present NIEL calculations.

The photoconductivity spectrum of electron and neutron irradiated n lightly doped GaAs

The spectral photoconductivity spectrum of lightly doped n GaAs exposed to electron and neutron irradiation is studied. From the temperature dependence of the photoconductivity, it is deduced that neutron irradiation induces a shallow donor level; photoluminescence experiments suggest that its energy lies 31 meV below the conduction band. Electron irradiation is about factor of 10 more effective than the neutron irradiation in reducing the ratio PC(17)/PC