Yoichi Kamiura

Chemical etching‐induced defects in phosphorus‐doped silicon

We have found with deep‐level transient spectroscopy that chemical etching introduced three electron traps, E1(0.11), E2(0.13), and E3(0.15), in the near‐surface region of phosphorus‐doped crystalline silicon. The results on depth profiles of these traps and carriers suggested the donor character of the traps, but they hardly exhibited the Poole–Frenkel effect. From their correlations with carbon and oxygen, we propose a tentative identification that E1 and E2 traps arise from two kinds of hydrogen‐oxygen‐carbon complexes and the E3 trap arises from a hydrogen‐carbon complex. Hydrogen is assumed to be adsorbed on the silicon surface during chemical etching and diffuse into the interior of the crystal during the subsequent evaporation and sample storage processes to be trapped at two kinds of oxygen‐carbon complexes and substitutional carbon to form the traps. The annealing behavior of E2 and E3 traps in the dark were studied in detail. Their densities were increased at temperatures of 70–90 °C and subsequ...

A new family of thermal donors generated around 450 °C in phosphorus‐doped Czochralski silicon

We have discovered a new family of oxygen‐related double donors [new thermal donors (NTD’s)] generated around 450 °C in phosphorus‐doped Czochralski silicon by combining deep‐level transient spectroscopy with Hall measurements. This new family was well distinguished from the normal family of thermal donors (TD’s) currently studied so far. Our results have shown that both families of thermal donors exhibit qualitatively the same kinetic behavior. Namely, as the annealing time increases, their ionization energy of levels continuously decrease with their densities increasing until the maxima and then become constant with their densities decreasing. However, there are significantly quantitative differences between the both families; NTD’s have shallower levels, considerably smaller generation rates, and higher thermal stability than TD’s. Sufficiently prolonged annealing for more than 105 min around 450 °C or short donor‐killing annealing for 20 min at 650 °C completely annihilates TD’s, leaving only NTD’s, o...

Photo-Enhanced Activation of Hydrogen-Passivated Magnesium in P-Type GaN Films

We studied the effect of UV-light irradiation on annealing of as-grown Mg-doped GaN films by resistivity and Hall measurements. The annealing temperature where the resistivity reduction due to the electrical activation of hydrogen-passivated Mg occurred with the increase of hole density and the decrease of hole mobility, was reduced from 550 to 450°C by the irradiation of UV light with a peak wavelength around 350 nm. This suggests that electronic excitation reduces the thermal stability of Mg-H complexes in GaN.

Hydrogen diffusivities below room temperature in silicon evaluated from the photoinduced dissociation of hydrogen–carbon complexes

We have evaluated hydrogen and deuterium diffusivities in silicon below room temperature (220–270 K) by analyzing the kinetics of photoinduced dissociation of a chemical etching introduced hydrogen (deuterium)–carbon complex. Under sufficiently strong illumination, the annihilation rate of the complex was proportional to the phosphorus density, indicating that the rate‐determining step is the diffusion of hydrogen (deuterium) to phosphorus atoms. Applying the diffusion‐controlled reaction theory, we have evaluated the diffusion coefficients as 7×10−2exp(−0.54 eV/kT) cm2 s−1 for hydrogen and 5×10−3exp(−0.49 eV/kT) cm2 s−1 for deuterium, being in good agreement with the extrapolation of the high‐temperature diffusion data of A. Van Wieringen and N. Warmoltz [Physica 22, 849 (1956)].

Observation of iron pileup and reduction of SiO2 at the Si‐SiO2 interface

It was found by secondary‐ion mass spectrometry in‐depth profiling technique that approximately 1×1020 iron atoms/cm3 accumulated at the Si‐SiO2 interface of oxidized silicon crystals where iron was introduced by the indiffusion prior to the oxidation at 1000 °C and above. The origin of iron accumulation is ascribed to the iron precipitation from the bulk silicon. It was also found that iron atoms that diffuse in through the bulk from the lapped backside of a preoxidized sample were trapped and aggregated at the front Si‐SiO2 interface. An interesting observation is shown that the above indiffusing iron also entered into the oxide region near the interface possibly to reduce SiO2.

Deep center related to hydrogen and carbon in p‐type silicon

We have found a hole trap related to hydrogen and carbon in p‐type crystalline silicon after hydrogen and deuterium injection by chemical etching and plasma exposure. It was found from deep‐level transient spectroscopy that this center is located at 0.33 eV above the valence band and shows no Poole–Frenkel effect in electric fields lower than 6×103 V/cm. The depth profiling technique using deep‐level transient spectroscopy indicated that this center is distributed over the range 1–7 μm from the surface with densities of 1011–1013 cm−3, depending on the hydrogenation method. On the other hand, secondary ions mass spectroscopy revealed that the majority of deuterium injected into silicon exists within a much shallower region less than 60 nm from the surface with higher densities of 1018–1020 cm−3. We have therefore concluded that the majority of injected hydrogen stays in the near‐surface region probably in the form of a molecule and larger clusters and only the minority diffuses into the bulk in an atomic ...

Copper-Related Deep Levels and Their Annealing Kinetics in Germanium

Four copper-related hole traps, H1(0.04), H2(0.09), H3(0.23) and H4(0.33), have been observed in heat-treated germanium by deep-level transient spectroscopy. H1 and H4 traps are identified as singly and doubly ionized acceptor levels of substitutional copper, Cus. Annealing around 200°C caused annihilation of H2 and H3 traps with a correlated increase in Cus density. Annealing kinetics have been studied by analyzing resistivity data by the reaction scheme, H2\rightleftharpoonsCus+H3 and H3→sinks (dislocations and the sample surface). This analysis has the yielded 6×10-3 exp (-0.35[eV]/kT) cm2s-1 for the diffusion coefficient of the H3 trap, which agrees well with that of the interstitial copper, Cui, determined by previous tracer experiments. From this and the donor character of the H3 trap, we have identified the H3 donor and H2 acceptor as Gui and the Gui–Gus pair, respectively.

Evidence for the recombination‐enhanced dissociation of a hydrogen‐carbon complex in silicon

We have recently found that hydrogen injected into n‐type crystalline silicon by chemical etching not only passivated phosphorus but also electrically activated substitutional carbon by forming a hydrogen‐carbon complex with a donor level at Ec−0.15 eV. This article shows that the complex was annihilated by above‐gap excitation near and below room temperature only outside the depletion layer of the Schottky structure under the application of various reverse bias voltages. This clearly proves that the hydrogen‐carbon complex is dissociated via the recombination‐enhanced defect reaction.

Electronically induced instability of a hydrogen-carbon complex in silicon and its dissociation mechanism

We studied, by deep-level transient spectroscopy (DLTS), the dissociation mechanism of a hydrogen-carbon (H-C) complex, which has a donor level at E c-0.15 eV and acts as an electron trap in crystalline silicon. On the basis of our results and a previously proposed atomic model of the H-C complex, in which the hydrogen atom resides inside a silicon-carbon bond, we have proposed the following dissociation mechanism. The complex is stable in the positive charge state, and to dissociate it needs a hydrogen jump with an activation energy of 1.3 eV to break the bond with carbon and silicon. The complex becomes neutral by capturing an electron from the conduction band or accepting an electron directly from the valence band under electronic excitation, and is consequently dissociated at an activation energy of 0.5 eV due to the loss of binding. Strong evidence for the existence of the negative charge state of hydrogen in crystalline silicon is also presented.

Copper‐related deep acceptor in quenched germanium

New deep acceptors (DA) at Ev+80 meV together with contaminating substitutional copper (Cus) were produced in Ge by the quenching from 700 °C. Annealing around 260 °C caused these acceptors to disappear leaving an equal additional Cus density, giving rise to a decrease in hole mobility at 77 K. The annealing process obeys first‐order kinetics with an activation energy of 1.3 eV. Annealing behavior consistently explains the so‐called reverse annealing of quenching‐induced conductivity changes that have often been observed by various investigators. In the as‐quenched state, the DA density is completely proportional to the Cus density, which was varied at 700 °C from 3×1013 to 3×1015 cm−3 using the techniques of gettering and diffusion of copper. The 1.5 MeV electron irradiation to a total dose of 5×1014 electrons/cm2 slightly below room temperature induced the DA acceptors once annihilated by the preceding annealing to reappear in a density of 2×1013 cm−3. The most probable defect model for the DA acceptor ...