Tokue Matsumori

Photoluminescence of very dilutely C+ ion‐implanted GaAs

Very dilute C+ (carbon) ion implantations were carried out for extremely pure GaAs wafers grown by molecular beam epitaxy (MBE). Low‐temperature photoluminescence measurements revealed that at least five sharp new emission lines are commonly formed near bound exciton emission region by the introduction of C for the dose range between 1015 and 1017 cm−3. It was for the first time demonstrated that the most dominant line among the above emission is identical to the g line in defect‐induced bound exciton emission series which are frequently observed in rather impure MBE‐grown or metalorganic chemical vapor deposition (MOCVD)‐grown GaAs samples.

Photoluminescence spectra of undoped GaAs grown by molecular‐beam epitaxy at very high and low substrate temperatures

The incorporation mechanisms of residual impurities in GaAs layers grown by molecular‐beam epitaxy has been investigated by high‐resolution photoluminescence (PL) spectroscopy at 2 K. A systematic study of near‐band‐edge emissions of undoped GaAs layers grown at a wide range of growth temperatures (Tg), 470–750 °C, demonstrates that PL spectra related with residual impurities are significantly dependent upon Tg. It was found that maximum emission intensity of free exciton is obtained at Tg ∼550 °C, and the minimum impurity incorporation is established at Tg of 550–650 °C.

INFLUENCE OF THE IMPLANTATION OF C+ IONS ON PHOTOLUMINESCENCE AND ELECTRICAL PROPERTIES OF GAAS

Ion implantation of carbon (C) into extremely pure GaAs grown by molecular‐ beam epitaxy is carried out over a wide range of C atomic concentrations [C], from 1×1016 to 5×1019 cm−3. The impurity levels in the implanted layer are investigated by using photoluminescence (PL) and Hall‐effect measurements. Below the well‐defined exciton luminescence lines, one broad emission band, namely [g‐g], is found to be exclusively attributable to acceptor impurities and is dominant for [C] lower than 3×1017 cm−3. However, a decrease of its intensity and a ‘‘locking’’ of its emission energy shift is observed for [C] higher than this value. A carrier transport mechanism is found to be relevant to the C acceptor level for C atoms at As sites, and deep acceptors caused by residual radiation defects. The concentration of substitutional C atoms is nearly coincident with [C] up to 1×1017 cm−3, but the activation efficiency for [C]=1×1018 cm−3 decreases by about 13%. The decrease of overall PL intensity and the locking of the ...

New emission lines in highly carbon ion-implanted GaAs

Abstract Ion-implantation of carbon (C + ) into very pure GaAs samples grown by molecular beam epitaxy (MBE) was carried out. Low temperature photoluminescence (PL) measurements at 2 K were performed under a very low excitation condition. The results as functions of dose, annealing temperature and excitation intensity reveal that the incorporation of C makes at least seven radiative emission levels near the band-edge. The controversial origin of so-called defect-induced bound excitons (DIBE) commonly observed in rather impure GaAs grown by MBE was clearly explained by the intentional introduction of C ions in the sense that only a few emission lines observed on the higher energy side of DIBE are directly related with the C impurity, and the remaining emission is connected with defects, presumably induced by the simultaneous presence of C and O(oxygen) atoms.

Conditions for the formation of defect‐induced bound exciton emissions in GaAs grown by molecular beam epitaxy

Conditions for the formation of defect‐induced bound exciton (DIBE) emissions in GaAs were investigated by molecular beam epitaxial method. Growth was made on both A‐ and B‐polarity substrates with (321), (221), and (211) orientations. For A‐polarity samples, (321)A and (211)A presented pronounced DIBE emissions. (221)A, however, exhibited no DIBE emission, instead it presented a dominant carbon donor‐carbon acceptor pair emission together with a small hump due to carbon donor‐related bound exciton emissions. For B‐polarity specimens, DIBE was completely vanished in all the three samples. It was theoretically demonstrated that DIBE is formed only when double‐handed Ga adatom site is existing.

Anomalous photoluminescence and raman scattering behavior in heavily Mg+ ion-implanted InP

Mg+ ions were implanted into highly pure InP grown by the liquid encapsulated Czochralski (LEC) method in which the Mg concentration [Mg] was varied between 1×1015 cm−3 and 3×1020 cm–3. Two annealing methods were used: furnace annealing (FA) up to 740° C and flash lamp annealing (rapid thermal annealing, RTA) up to 900° C. For characterization, photoluminescence (PL) spectra were measured between 2K and room temperature together with Raman scattering measurements at room temperature. An emission designated by g, which was attributed to a novel energy state of an isolated acceptor, was found to be produced for a rather low value of [Mg]. In addition, a broad emission denoted by [g−g], which was ascribed to acceptor-acceptor pairs, was observed below bound exciton emissions for moderate values of [Mg]. These features were quite similar to those previously observed in acceptor-doped GaAs when the background concentration of donors is extremely low. Two additional novel emissions located far below the band-to-acceptor emission were also obtained, and each showed a remarkable energy shift towards lower energy with increasing [Mg]. The binding energies of these emissions were estimated from the temperature dependence of PL spectra and the results suggest that they are complex-type radiative recombination centers, presumably donor-acceptor-type centers. A strong broad emission centered near the band-to-acceptor emission was observed for [Mg]=3×1020 cm−3. This observation indicates a formation of a new material between In, P and Mg, which was also attested by the appearance of a new TO-like Raman signal for [Mg] greater than 1×1019 cm−3. A substantial difference of PL and Raman spectra was revealed for the two annealing methods, suggesting that the annealing behaviour of ion-implanted InP should be investigated more extensively in order to establish reliable annealing procedures.

Liquid‐phase epitaxy of heavily Mg‐doped GaAs: Formation of a new near‐band‐edge emission exclusively pertinent to acceptor impurities

Liquid‐phase epitaxy (LPE) of Mg‐doped GaAs was carried out. An extremely heavy doping was accomplished with a maximum net hole concentration of 1.31×1019 cm−3. A systematic investigation of photoluminescence spectra was performed as a function of hole concentration, which revealed that a newly discovered emission characterizing acceptor impurities can be obviously recognized also in LPE‐grown samples in spite of the fact that the selective optical compensation effect among doped acceptors and residual donors presumably coming from Si of the LPE quartz tube is supposed to be comparatively strong. The red shift of this emission energy with increasing hole concentration and its locking at high hole concentration were discussed theoretically by introducing a preliminary model, i.e., a pair between excited‐state acceptors.

Photoluminescence from InP heavily ion-implanted with Mg+

Abstract Ion-implantation of magnesium into extremely pure InP grown by the liquid-encapsulated Czochralski method was carried out with magnesium concentrations [Mg] ranging from 1 × 1015 to 3 × 1020 cm−3 with a maximum energy of 400 keV. Low temperature photoluminescence and Raman scattering measurements were performed on these samples. A new state of excitions bound to what was presumed to be a new type of acceptor g and an emission attributed to acceptor-acceptor pairs [g-g] were found below the bound exciton emission series. Two novel emissions located far below the band-to-acceptor emissions were also observed, and these showed remarkable energy shifts towards the lower energy side with increasing [Mg]. With heavily implanted samples, a strong broad emission of a new type was observed in the vicinity of the band-to-acceptor emissions.

Photoluminescence of undoped, N+‐implanted and C+‐implanted AlAs grown by molecular beam epitaxy

Low‐temperature photoluminescence studies of undoped, N+ (nitrogen)‐implanted and C+ (carbon)‐implanted AlAs grown by molecular beam epitaxy are reported. It was experimentally demonstrated that a dominant emission temporarily denoted by A, observed at 13 meV below the indirect excitonic band gap, Eg,ind(X), is closely related with N isoelectronic impurity atoms. It was also found that the A emission accompanies many one‐phonon and two‐phonon replicas, among which the longitudinal optical phonon replica is predominant. Carbon atoms were determined not to be principal residual impurities in undoped AlAs. The two conspicuous C‐related emissions were revealed by the intentional incorporation of C atoms, which are situated at 60 and 64 meV below Eg,ind(X).

Ion implantation of isoelectronic impurities into InP

Ion-implanted InP with several kinds of isoelectronic impurities (B+, N+, P+, As+, Sb+ and Bi+) was characterized by photoluminescence (PL) and Raman scattering spectroscopies. The ion concentration was varied between 1 × 1015 and 1 × 1020 cm−3. Remarkably broad emissions extending far above the band gap of InP were observed when B+ or N+ was singly implanted to a concentration of 1 × 1020 cm−3. They appeared more intensively when InP was ion-implanted with B+ as well as with N+ to respective concentrations greater than 1 × 1019 cm−3. These features explicitly demonstrate that a new material was produced by introduction of the same amount of group, III and V elements, suggesting that a mixed compound semiconductor between B, N, In and P, i.e., (BN)x(InP)1−x is fabricated. The formation of new materials was also shown by Raman scattering measurements. It is indicated that high dose ion implantation of isoelectronic elements of small mass is promising method to produce mixed crystal semiconductors. For As+, Sb+ or Bi+ ion-implanted InP, a distinct PL emission was commonly observed below bound exciton emissions for concentrations around 1 × 1016 cm−3. These are, to our knowledge, the first-reported radiative recombination centers attributed of these isoelectronic impurities. Bi was found to form a sharp PL emission below bound exciton emissions, suggesting that implanted Bi becomes an efficient recombination center.