Akihito Taguchi

Intra‐4f‐shell luminescence excitation and quenching mechanism of Yb in InP

The excitation and quenching mechanism of intra‐4f‐shell luminescence of Yb ions incorporated in an InP host is discussed. The discussion is based on experimental results of photoluminescence excitation spectra and photoluminescence time‐decay curves for crystals grown by metalorganic chemical vapor deposition and liquid‐phase epitaxy. The present as well as previously reported experimental results for samples grown by various methods can be consistently interpreted by considering a recently reported Yb‐related acceptorlike electron trap near the conduction‐band edge and by taking into account the shallow donor and acceptor as well as Yb concentrations in the samples. A model is proposed which describes the Yb intra‐4f‐shell excitation and quenching mechanisms for samples with various concentrations of the impurities.

Selective formation of an efficient Er‐O luminescence center in GaAs by metalorganic chemical vapor deposition under an atmosphere containing oxygen

To investigate the effects of oxygen codoping on Er luminescence centers in GaAs, we grew Er‐doped GaAs by low‐pressure metalorganic chemical vapor deposition (MOCVD) and measured the photoluminescence spectrum due to the intra‐4f‐shell transition of Er. The spectrum of a sample grown in a pure hydrogen atmosphere was complicated, showing many lines and bands. The spectrum of a sample grown in a hydrogen atmosphere containing 0.2 ppm oxygen, on the other hand, was simple and had few lines. The spectrum of the oxygen‐codoped sample showed higher peak intensities as well as higher integrated luminescence intensity in the 1.5–1.6 μm region. Secondary‐ion mass spectroscopy revealed that the oxygen‐codoped sample had a higher concentration of oxygen, indicating the formation of an Er‐O complex center. One kind of optically active efficient Er‐O complex luminescence center can, therefore, be selectively formed under suitable MOCVD growth conditions.

Atomic configuration of the Er‐O luminescence center in Er‐doped GaAs with oxygen codoping

This article investigates the structure of an Er luminescence center in GaAs by using its intra‐4f‐shell luminescence spectrum as an atomic probe to identify the atomic configuration. This Er center is formed in GaAs by metalorganic chemical vapor deposition with O codoping and the center shows a high efficiency and a sharp luminescence spectrum under above‐band‐gap photoexcitation. A single luminescence line in the spectrum of a GaAs:Er,O splits into more than eight lines in the spectrum of Al0.01Ga0.99As:Er,O. This drastic change due to the addition of 1% Al can be explained by assuming that, because of the high tendency of Al atoms to react with O atoms, the Al atoms preferentially occupy the nearest‐neighbor Ga sites of two O atoms, both of which are coupled with the Er atom. Based on the luminescence spectra and additional experiments of Rutherford backscattering and secondary ion mass spectroscopy, we propose that the structure of the Er luminescence center under study is Er occupying the Ga sublatt...

A new theoretical approach to adsorption–desorption behavior of Ga on GaAs surfaces

Abstract We propose a new theoretical approach for studying adsorption–desorption behavior of atoms on semiconductor surfaces. The new theoretical approach based on the ab initio calculations incorporates the free energy of gas phase; therefore we can calculate how adsorption and desorption depends on growth temperature and beam equivalent pressure (BEP). The versatility of the new theoretical approach was confirmed by the calculation of Ga adsorption–desorption transition temperatures and transition BEPs on the GaAs (0 0 1) - (4×2) β2 Ga-rich surface. This new approach is feasible to predict how adsorption and desorption depend on the growth conditions.

Theoretical approach to influence of As2 pressure on GaAs growth kinetics

Abstract The newly developed first-principles calculation based computational method incorporating chemical potential of As 2 gas is applied to understand the influence of As 2 pressure on GaAs growth kinetics under the molecular beam epitaxy growth conditions with high As 2 pressures where the c(4×4) reconstructed structure appears on the surface. The calculated results suggest that the chemical potential of As 2 gas increases with As 2 pressure, which suppresses As 2 (As-dimer) desorption or extends As 2 surface lifetime. This induces the decrease of GaAs growth rate, because GaAs layer-by-layer growth does not proceed without As 2 desorption on the As-rich c(4×4) surface.

Multiphonon‐assisted energy transfer between Yb 4f shell and InP host

The energy transfer mechanism between an Yb 4f shell and an InP host was investigated, assuming that a nonradiative multiphonon process assists the energy transfer. The values of the energy involved in the energy transfer were determined from the results of optical and electrical experiments. Rate equations were solved to obtain the temperature dependence of the Yb intra‐4f‐shell luminescence decay time. The calculated results and the experimentally obtained temperature dependence agree well. The calculated temperature dependence of the Yb intra‐4f‐shell luminescence intensity also agrees with the experimental measurements. These results strongly suggest that phonon absorption and emission compensate the energy mismatch in the energy transfer processes. The calculations also indicate that the thermal quenching phenomenon is mainly determined by the energy mismatch between the recombination energy of an electron and a hole and the Yb 4f‐shell energy between the excited and ground states. On the basis of th...

Theoretical investigation of nitrogen-doping effect on vacancy aggregation processes in Si

The nitrogen-doping effect on vacancy aggregation in Si is studied by comparing total energies of various complexes of nitrogen atoms and Si vacancies in terms of first-principles calculations. Two nitrogen atoms are found to form a stable complex with two Si vacancies, strongly suggesting that a supersaturation of “isolated” Si vacancies in growth cooling can be suppressed. The delayed void formation observed in N-doped Czochralski Si indeed supports this suggestion.

Direct verification of energy back transfer from Yb 4f‐shell to InP host

We report direct verification of energy back transfer from a Yb 4f‐shell to an InP host, which has been proposed as a quenching mechanism for the intrinsic thermal quenching of intra‐4f‐shell luminescence. Photoluminescence time decay of the band‐edge related luminescence for a Yb‐doped InP sample was examined. In the temperature region from 100 to 120 K, it was observed that the luminescence time‐decay curve is composed of two exponential decay components. The decay‐time constant of the slower component in the band‐edge related luminescence is the same as that in the Yb 4f‐shell luminescence. This fact clearly shows that there is an energy transfer between the Yb 4f‐shell electronic state and the InP host electronic state, and the energy back‐transfer mechanism is the cause of the intrinsic thermal quenching of the Yb intra‐4f‐shell luminescence.

TRAP LEVEL CHARACTERISTICS OF RARE-EARTH LUMINESCENCE CENTERS IN III-V SEMICONDUCTORS

We have applied a multiphonon‐assisted energy transfer model, which has been verified for the Yb‐doped InP system, to Er‐doped GaAs, Nd‐doped GaP, and Nd‐doped GaAs. By applying this model, the temperature dependence of the decay time of the 4f‐shell luminescence can be calculated using two parameters. One parameter is the energy transfer probability between the rare‐earth 4f shell and the semiconductor host, and the other is the energy which has to be compensated for in the energy transfer processes. The values of these two parameters were determined by fitting the calculated temperature dependence to the experimentally obtained results. The calculated temperature dependences fit with the experimental results well, showing that the energy transfer mechanism in these materials is similar to that in InP:Yb. The estimated values of energy which have to be compensated for enable us to estimate the energy level positions responsible for the rare‐earth intra‐4f‐shell luminescence. The values of the transition ...

Thermal quenching mechanism of Yb intra-4f-shell luminescence in InP

Thermal quenching mechanism of Yb intra‐4f‐shell luminescence were clarified by studying the temperature dependences of electrical and optical properties of Yb‐doped InP samples. The quenching mechanism which depends on shallow donor concentration was found by comparing temperature dependences of Yb 4f‐shell luminescence and free‐carrier concentration. This mechanism is a localized Auger effect and is efficient below about 70 K in samples having a larger donor concentration than Yb concentration. At higher temperatures, another quenching mechanism was found to be efficient which does not depend on donor concentration. This quenching of Yb intra‐4f‐shell luminescence is accompanied by some increase of band‐edge related luminescence. This phenomenon is explained by the energy back‐transfer mechanism from the excited Yb 4f‐shell to the InP host. Although an importance of the free‐carrier Auger effect has been suggested in conducting materials, we propose that above two mechanisms dominate the quenching of th...