Methods for the doping of silicon layers in growth by sublimation MBE

Epitaxial layers doped with various impurities were grown by sublimation MBE on Si (100) substrates. Doping with phosphorus was controlled at electron densities ranging from 2×10¹³ to 10¹⁹ cm^?3. A high dopant concentration of ～10²⁰ cm^?3 was obtained from the evaporation of partly molten Si sources. It shown that the type and concentration of an impurity in the sublimation MBE process can be controlled by the fabrication of multilayer p ⁺?n ⁺ structures.     

Si Doping of GaN in Hydride Vapor-Phase Epitaxy

Growth of GaN boules by hydride vapor-phase epitaxy (HVPE) is very attractive for fabrication of GaN substrates. Use of dichlorosilane as a source for Si doping of bulk GaN is investigated. It is shown that no tensile strain is incorporated into mm-thick, Si-doped GaN layers on sapphire substrates if the threading dislocation density is previously reduced to 2.5 × 10⁷ cm^?2 or below. High-quality GaN layers with electron densities up to 1.5 × 10¹⁹ cm^?3 have been achieved, and an upper limit of about 4 × 10¹⁹ cm^?3 for Si doping of GaN boules was deduced considering the evolution of dislocations with thickness. A 2-inch, Si-doped GaN crystal with length exceeding 6 mm and targeted Si doping of about 1 × 10¹⁸ cm^?3 is demonstrated.     

Decrease in the binding energy of donors in heavily doped GaN:Si layers

The properties of Si-doped GaN layers grown by molecular-beam epitaxy from ammonia are studied by photoluminescence spectroscopy. It is shown that the low-temperature photoluminescence is due to the recombination of excitons bound to donors at Si-atom concentrations below 10¹⁹ cm^?3. At a Si-atom concentration of 1.6 × 10¹⁹ cm^?3, the band of free excitons is dominant in the photoluminescence spectrum; in more heavily doped layers, the interband recombination band is dominant. A reduction in the binding energy of exciton-donor complexes with increasing doping level is observed. With the use of Haynes rule, whereby the binding energy of the complex in GaN is 0.2 of the donor ionization energy E _D , it is shown that E _D decreases with increasing Si concentration. This effect is described by the dependence {ie1134-1}, where E _D ^otp is the ionization energy of an individual Si atom in GaN. The coefficient that describes a decrease in the depth of the impurity-band edge with increasing Si concentration is found to be α = 8.4 × 10^?6 meV cm^?1.     

The electrical characteristics of InP implanted with the column IV elements

A study of the electrical characteristics of InP implanted with C, Si, Ge and Sn demonstrates that all of these column IV elements are donors, although the net electrical activation achieved with the light ion C was only about 5%. Samples implanted at temperatures of 150–200°C generally had lower sheet resistivities, higher mobilities and except for high doses, higher sheet carrier concentrations than those done at room temperatures. Implants at 150–200°C with 1 × 10¹⁴cm^?2 of the heavier ions, Si, Ge or Sn, resulted in layers with sheet carrier concentrations of 7.8 × 10¹³, 5.6 × 10¹³ and 4.7 × 10¹³cm^?2, respectively. Carrier concentration profiles of samples implanted at 200°C with 1 × 10¹⁴cm^?2 of Si agreed reasonably well with LSS theory. Higher doses gave rise to substantial diffusion of the implanted Si, whereas room temperature implants showed poor activation near the surface.     

Isotopic effects in the infrared absorption spectra of electrically active impurities in silicon 28, 29, and 30 with high isotopic enrichment

The results of studying the IR absorption spectra of shallow donors and acceptors in high-purity stable ²⁸Si(99.99%), ²⁹Si(99.92%), and ³⁰Si(99.97%) isotope single crystals grown by the method of float zone melting were reported. The content of residual boron, phosphorus, and arsenic impurities in the studied single crystals was determined with a detection limit of 1 × 10¹², 4 × 10¹¹, and 1 × 10¹² at./cm³, respectively. The results of the IR spectroscopic estimation of the content of shallow donors and acceptors were in good agreement with the data obtained from the Hall effect measurements for the concentration of free charge carriers. The parameters of the absorption lines of boron and phosphorus impurities in the single crystal of silicon isotopes were studied. The change in the isotope composition of silicon was shown to lead to the shift of the energy spectrum of shallow impurity sites towards higher energies with an increase in the atomic weight of an isotope.     

Instability of characteristics of SiC detectors subjected to extreme fluence of nuclear particles

The operation of detectors irradiated with 8-MeV protons at a fluence of 3 × 10¹⁴ cm^?2 has been studied. The detectors were based on modern CVD-grown n-4H-SiC films with a concentration of uncompensated donors equal to ～2 × 10¹⁴ cm^?3 and a thickness of 55 μm. The high concentration of primary radiation defects (～2 × 10¹⁷ cm^?3) determined the deep compensation of the films. The basic characteristics of the detectors—pulse amplitude and resolution—exhibited temporal instability. This effect is due to prolonged capture of nonequilibrium carriers by radiation centers and the resulting appearance of a polarization voltage in the bulk of the detector. The kinetics of attainment of steady values by the quantities specified above was analyzed.     

Incorporation and Activation of Arsenic Dopant in Single-Crystal CdTe Grown on Si by Molecular Beam Epitaxy

We report the use of molecular beam epitaxy to achieve p-type doping of CdTe grown on Si(211) substrates, by use of an arsenic cracker and post-growth annealing. A high hole density in CdTe is crucial for high efficiency II–VI-based solar cells. We measured the density of As in single-crystal CdTe by secondary ion mass spectroscopy; this showed that high As incorporation is achieved at low growth temperatures. Progressively higher incorporation was observed during low-temperature growth, presumably because of degradation of crystal quality with incorporation of As at such defect sites as dislocations and defect complexes. After As activation annealing under Hg overpressure, hole concentrations were obtained from Hall measurements. The highest doping level was ～2.3 × 10¹⁶ cm^?3, and near-10¹⁶ cm^?3 doping was readily reproduced. The activation efficiency was ～50%, but further optimization of the growth and annealing conditions is likely to improve this value.     

Effect of extreme radiation fluences on parameters of SiC nuclear particle detectors

Detectors based on modern CVD-grown films were irradiated with 8 MeV protons at a fluence of 3 × 10¹⁴ cm^?2. The concentration of primary radiation defects was ～10¹⁷ cm^?3, which is three orders of magnitude higher than the concentration of the initially present uncompensated donors. The resulting deep compensation of SiC enabled measurements of detector parameters in two modes: under reverse and forward bias. The basic parameters of the detectors degraded by no more than a factor of 1.7, compared with the fluence of 1 × 10¹⁴ cm^?2. However, there appeared a polarization voltage, which indicates that a space charge is accumulated by radiation defects.     

Dislocation behavior in heavily germanium-doped silicon crystal

Dislocation-free heavily Ge-doped Czochralski (CZ)-Si crystal growth using a heavily Ge-doped Si seed has been investigated. Dislocations due to thermal shock were suppressed in a seed 7×7 mm² in cross-section when Ge concentration in the seed exceeded 9×10¹⁹ atoms/cm³. When Ge concentration in the grown crystal was 5.7×10²⁰ atoms/cm³, cellular growth occurred, and this concentration was a limit for heavily Ge-doped Si single crystal growth with a growth rate of about 1 mm/min. Resistivity in the crystal results in B or P doping could be controlled precisely in spite of using a heavily Ge-doped Si seed for growing a dislocation-free CZ-Si crystal without Dash necking.     

Electrical properties and low-temperature photolumincesence of Si-doped CdTe crystals

The CdTe:Si single crystals with Si concentration in the range of C _Si ⁰ =2×10¹⁸–5×10¹⁹ cm^?3 are grown by the Bridgman-Stockbarger method. The samples were of the n-and p-type with electrical conductivity σ=2×10^?1–8×10^?9 Ω^?1 cm^?1. Being heated in the temperature range 300–440 K, the p-CdTe crystals were annealed, and their conductivity decreased. The shape of the low-temperature (5–20 K) photoluminescence spectra of the samples are indicative of their high structural quality. The specific feature of the emission of the CdTe:Si crystals is its decrease in the intensity of all lines induced by donors as the samples are cut progressively closer to the ingot top. The results obtained indicate that the Si impurity, in contrast with Ge, Sn, and Pb, does not exhibit the compensating and stabilizing effect in CdTe.     

Highly transparent and conducting zinc oxide films deposited by activated reactive evaporation

Highly transparent and conducting undoped zinc oxide films have been obtained with a best resistivity of ～1.1 × 10^-3 Ω cm, a carrier density of ～1.5 × 10²⁰ cm^?3 and a mobility of ～38 cm²V^{?1s ?1}. These were produced by activated reactive evaporation at a deposition rate of 2 to 8Å/s with a substrate temperature ≤200° C. The films deposited by this process were found to have resistivities that were thickness independent and also were relatively insensitive to deposition parameters. In terms of conductivity, it was found that films deposited at higher temperatures (T > 300°+ C) were always inferior to the films deposited below 200° C. High temperature vacuum annealing (350° C) significantly degraded the resistivity of the undoped films deposited at low temperature; this was attributable to a drop in both the electron concentration and the mobility. Aluminum doping was found to be able to stabilize the electron concentration while the drop in mobility was found to be related to the choice of substrate.     

Ge/Si photodiodes with embedded arrays of Ge quantum dots forthe near infrared (1.3–1.5 µm) region

A method has been devised for MBE fabrication of p-i-n photodiodes for the spectral range of 1.3–1.5 µm, based on multilayer Ge/Si heterostructures with Ge quantum dots (QDs) on a Si substrate. The sheet density of QDs is 1.2×10¹² cm^?2, and their lateral size is ～8 nm. The lowest room-temperature dark current reported hitherto for Ge/Si photodetectors is achieved (2×10^?5 A/cm² at 1 V reverse bias). A quantum efficiency of 3% at 1.3 µm wavelength is obtained.     

Carrier Lifetimes of Iodine-Doped CdMgTe/CdSeTe Double Heterostructures Grown by Molecular Beam Epitaxy

Iodine-doped CdMgTe/CdSeTe double heterostructures (DHs) have been grown by molecular beam epitaxy and studied using time-resolved photoluminescence (PL), focusing on absorber layer thickness of 2 μm. The n-type free carrier concentration was varied to ～7 × 10¹⁵ cm^?3, 8.4 × 10¹⁶ cm^?3, and 8.4 × 10¹⁷ cm^?3 using iodine as dopant in DHs. Optical injection at 1 × 10¹⁰ photons/pulse/cm² to 3 × 10¹¹ photons/pulse/cm², corresponding to initial injection of photocarriers up to ～8 × 10¹⁵ cm^?3, was applied to examine the effects of excess carrier concentration on the PL lifetimes. Iodine-doped DHs exhibited an initial rapid decay followed by a slower decay at free carrier concentration of 7 × 10¹⁵ cm^?3 and 8.4 × 10¹⁶ cm^?3. The optical injection dependence of the carrier lifetimes for DHs was interpreted based on the Shockley–Read–Hall model. The observed decrease in lifetime with increasing n is consistent with growing importance of radiative recombination.     

Electrical measurements on ion-implanted LPCVD polycrystalline silicon films

The electrical conduction properties of ion implanted polycrystalline silicon films have been studied. The polysilicon films were deposited by pyrolysis of silane at 647°C in LPCVD system onto oxide-coated silicon wafers to a thickness of 0.6 μm. Dopants were itroducd by implanting with boron or phosphorus ions, accelerated to 145 keV; doses ranged from 1 × 10¹² cm^?2 to 1 × 10¹⁵ cm^?2. Film resistivities spanning 8 orders of magnitude were obtained using this doping range. Current-voltage characteristics of polysilicon resistors were measured at temperatures ranging from 24 to 140°C. The associated barrier heights and activation energies were derived. The grain-boundary trapping states density was estimated to be 5 × 10¹² cm^?2. We found that both dopant atom segregation and carrier trapping at the grain boundaries play important roles in polysilicon electrical conduction properties. However, within the dose range studies, the dopant atom segragation is most detrimental to the film conductivity for doses < 1 × 10¹³ cm^?2; as the dose is increased, carrier trapping effects become more pronounced for doses up to 5 × 10¹⁴ cm^?2. For doses ? 5 × 10¹⁴ cm^?2, conduction due to carriers tunneling through the potential barriers at grain boundaries has to be considered.     

Nanostructuring of crystalline grains of natural diamond using ionizing radiation

Crystalline grains of type IIa natural diamond (the average grain mass is ～1 mg) are studied after their irradiation with neutrons in a nuclear reactor at a neutron fluence of ～10²¹ cm^?2. The irradiation is found to bring about a decrease in the macroscopic density of the grains by 40%. A quadrature signal of electron spin resonance (ESR) with a gfactor equal to 2.00006 and a paramagnetic-relaxation time > 10^?5 s is detected for the first time. Metastable uncompensated electron spins residing at the inner surface of the nanovoids may be the cause of the appearance of this signal. A similar signal is also observed for C₆₀ fullerite powder. The results of an ESR spectroscopy study of the irradiated diamonds are consistent with data obtained from Raman scattering spectroscopy (the appearance of an anomalously broad band peaked at 950 cm^?1 instead of a narrow single line at 1332 cm^?1 in the initial sample) and electron microscopy (the appearance of nanostructuring). It is established that nanostructuring of diamond under the effect of ionizing radiation brings about the appearance of dc electrical conductivity with an activation energy of 0.17 eV in the temperature range 30 to 300°C.     

Microwave magnetoresistance of compensated p-Ge:Ga in the region of the insulator-metal phase transition

The microwave magnetoresistance (MR) of neutron transmutation doped (moderately compensated) Ge:Ga in the insulator-metal transition region was studied using ESR technique. As the hole concentration increases, the MR mechanism changes in the insulator state near the phase transition point: the hopping conductivity that is characterized by the impurity wave-function contraction by the magnetic field is replaced by the state of weak localization. In the latter case, the temperature dependence of the diffusion coefficient is of great importance near the transition point (1.2×10¹⁷ cm^?3). This dependence decreases in the metallic state. In the metallic state, the diffusion coefficient is independent of temperature and the MR temperature dependence is described by the dephasing mechanism due to phonon scattering. The electron-electron interaction contribution to the dephasing time should be considered for heavier doping.     

The electrical and optical properties of InP irradiated with high integrated fluxes of neutrons

The results of studying the electrical properties and optical-absorption spectra of InP irradiated with fast neutrons (E > 0.1 MeV and D_f.n ≤ 10¹⁹ cm^?2) and full-spectrum reactor neutrons (D_th.n ≤ 2.1 × 10¹⁹ cm^?2; the ratio of the fluxes was ?_th.n/?_f.n ≈ 1) are reported. The variations in these properties resulting from postirradiation annealing at temperatures as high as 900°C are also studied. The results of the optical studies indicate that, in InP irradiated heavily with neutrons, free charge carriers appear only after annealing at temperatures higher than 500°C. The efficiency of neutron-initiated transmutational doping and the quality of transmutationdoped InP are assessed.     

Growth and characterization of Si doped vapor phase epitaxial GaAs for mesfet

This paper describes the Si-doping of GaAs that was grown using the AsCl₃:H₂:GaAs, Ga Chemical vapor deposition process. The doping sources were AsCl₃:SiCl₄ liquid solutions which proved to be highly reproducible for Si doping within the range, 1×1O¹⁶ to 2×10¹⁹ cm^?3. Incorporation of Si into the GaAs apparently occurs under near equilibrium conditions. This point is considered in detail and the consequences experimentally utilized to grow n, n+ bilayers using a single AsCl₃:SiCl₄ doping solution. Si impurity profiles based upon differential capacitance and SIMS data are presented. These can be very abrupt for n, n⁺ structures with order of magnitude changes occurring within 500 Å. For the 1×10₁₆ to 8×l0¹⁸ cm^?3 doped samples the mobilities at 78 and 298°K are comparable to the higher values reported for GaAs thin films grown by CVD. Power FET devices made from this material have demonstrated an output density of 0.86 watts/mm at 10 GHz.     

Charge fluctuations at the bonding interface in the silicon-on-insulator structures

Starting from the data of deep-level transient spectroscopy, the charge fluctuations at the interface between the top Si layer and buried insulator in Si-on-insulator structures are evaluated. The interface was prepared by bonding Si with the thermally oxidized substrate. The magnitude of fluctuations at the interface is found to be equal or exceed (1.5–2.0)×10¹¹ cm^?2 against the charge background of ～5×10¹¹ cm^?2 at this interface. It is shown that the fluctuations are most likely associated with the negative charge at the surface states rather than with the fluctuations of the fixed positive charge within oxide.     

Terahertz luminescence of GaAs-based heterostructures with quantum wells under the optical excitation of donors

Spontaneous emission from selectively doped GaAs/InGaAs:Si and GaAs/InGaAsP:Si heterostructures is studied in the frequency range of ～3–3.5 THz for transitions between the states of the two-dimensional subband and donor center (Si) under the condition of excitation with a CO₂ laser at liquid-helium temperature. It is shown that the population inversion and amplification in an active layer of 100–300 cm^?1 in multilayered structures with quantum wells (50 periods) and a concentration of doping centers N _D ≈ 10¹¹ cm^?2 can be attained under the excitation-flux density 10²³ photons/(cm² s).