Photoluminescence Patterns Research Articles

Anomalous brightening of donor-bound exciton photoluminescence caused by a pulsed electric field in n-GaAs

Anomalous brightening of photoluminescence (PL) spatial patterns has been investigated in an n-GaAs Corbino disk and an n-GaAs sample with the point contacts geometry under a pulsed electric field at 4.2 K. By applying a pulse voltage with the pulse width of 14.8 μs and the repetition frequency of 8.5 kHz, anomalous brightening of the PL patterns was observed for the nascent filaments as well as for the boundaries of the evolved filaments. A novel phenomenon of a long transient of the PL patterns was observed as a function of time τ. From the measurements of the PL spectra, the anomalous enhancement of the PL intensity is found to be caused by the impact ionization of the exciton bound to the neutral donor via the process e − +(D 0 , X)→2e − +(D + , X) or the process e − +(D 0 , X)→e − +D 0 +X .

Spatial pattern formation of optically excited carriers in photoconductive switches

We have spatially resolved the photoluminescence patterns emitted from a GaAs/Al0.3Ga0.7As quantum well after femtosecond laser excitation for different electric bias fields applied in the plane of the well. These patterns demonstrate substantially different electron–hole dynamics across the excitation laser spot. The density dependence of screening combines with the lateral variation of the carrier density to produce the observed effects. These results prove that the spatial variation of the carrier dynamics is to be taken into account for the optimization of photoconductive switches as ultrafast voltage pulse sources or THz emitters.

Variation with composition of the properties in ZnS xSe 1− x

Epitaxial layers of ZnS x Se 1− x ranging in composition x from 0.12 to 0.93 were grown on (1 0 0)Si substrates by atomic layer epitaxy (ALE). The epilayers are examined by photoluminescence and X-ray diffraction patterns at 300 K. The lattice match occurs at a composition of x=0.93.

Native and radiation-induced photoluminescent defects inSiO2: Role of impurities

We report photoluminescence (PL) data on amorphous ${\mathrm{SiO}}_{2}$ in the spectral range of the \ensuremath{\alpha} (4.3 eV), \ensuremath{\beta} (3.1 eV), and \ensuremath{\gamma} (2.7 eV) emissions excited with synchrotron radiation. Differently prepared and treated samples are compared. Neutron irradiation gives rise to PL features distinct from those observed both in unirradiated Ge-doped silica and in samples with other impurities. Our data suggest that the defect-formation processes determine the different PL patterns observed in ${\mathrm{SiO}}_{2},$ while the usually proposed distinction between Si- and Ge-like centers is not relevant.

Doping-induced selective area photoluminescence in porous silicon

The incubation time (ti) for the onset of porous Si formation by stain etching in HF:HNO3:H2O was observed to be a strong function of dopant type and concentration. For B-doped p-Si, ti increased significantly with substrate resistivity (ρ), from ∼0.5 min for 0.004 Ω cm to ∼9 min for 50 Ω cm. P-doped n-Si substrates exhibited a ti which decreased with increasing ρ, from ∼10 min for 0.15 Ω cm to ∼8 min for 20 Ω cm. We have utilized the difference in ti between n- and p-type Si to produce selective area photoluminescence (PL) by Ga+ focused ion beam (FIB) implantation doping and B+ broad beam implantation doping of n-type Si. Using 30 kV FIB Ga+ implantation, PL patterns with submicrometer resolution have been obtained for the first time.

Abrupt degradation of three types of semiconductor light emitting diodes at high temperature

Abrupt degradation of three types of semiconductor light emitting diodes (LED’s), Ga1−xAlxAs double-heterostructure (DH) LED’s, Ga1−xAlxAs/ GaAs DH LED’s, and LED-operated Ga1−xAlxAs/ GaAs DH lasers operated at high temperature, was studied by electroluminescence topography, photoluminescence topography, and transmission electron microscopy. The following results were obtained from all types of the diodes. Dark regions which included 〈100〉 dark-line defects (DLD’s) and/or 〈110〉 DLD’s were often observed in the electronluminescence or photoluminescence patterns of the active regions. Two phenomena were associated with this type of degradation as follows: (i) generation of high density of dislocations and dislocation loops (in some cases, stacking faults) by dislocation glide motion due to the relaxation of the stress concentrated in the active region. (ii) subsequent development of dislocation dipoles from the glided dislocations (often accompanied with many small dislocation loops). In some of the degraded diodes, the phenomenon (ii) did not occur. There might be a certain threshold for the phenomenon (ii).

Photoluminescence analysis of annealed silicon crystals

The photoluminescence (PL) technique has been used in the analysis of heat-treated silicon crystals to investigate the origin and the behavior of thermally induced defects. The PL measurements were made at liquid helium and liquid nitrogen temperatures on various groups of commercial wafers which were subjected to an isochronal annealing at a temperature between 450 and 1250 °C for 64 h. The PL results were compared with the results obtained by other characterization techniques, in particular, the infrared (IR) spectroscopy. After heat treatment at 450 °C, a new PL pattern appeared at 4.2 K, if the crystal contained a high concentration of oxygen. The new pattern is proved to be associated with the thermally induced donors. The PL and IR results classified Czochralski-grown wafers into two categories. Various heat treatments made a great change in the PL spectra for some wafer groups (category I), but a little change for the other wafer groups (category II). Correspondingly, the decrease in the interstitial oxygen concentration due to annealing was large for category I and small for category II. The PL intensity reduction at lower temperatures (600<T<900 °C) was closely correlated with the formation of silicon-oxygen complexes. It can be concluded that the Si-O complexes is produced with greater ease in category I than in category II. The variation in the configuration and/or the density of the Si-O complexes may induce the PL spectral change. Possible factors which separate the two categories are residual carbon and the thermal history of the crystal.

TEM observation of catastrophically degraded Ga1−xAlxAs double-heterostructure lasers

Defect structures of degraded GaAs/Ga1−xAlxAs double-heterostructure (DH) lasers applied with pulsed current under high current density are studied by transmission electron microscopy. Several kinds of defects are observed corresponding to the 〈110〉 dark-line defects which are observed in the photoluminescence patterns of the degraded DH lasers. They are arrays of dislocation tangles, nearly perfect dislocation networks, pipe-shaped defects with strong dark contrast, and simple dislocation dipoles. The former three kinds of dislocations are assumed to be caused by the propagation of molten zone due to local heating at the mirror surface and the last defects may be caused by thermal stress.

Photoluminescence Observation of Defects in Silicon

Two simple, rapid and nondestructive methods of evaluating defects in silicon are developed. These methods are based on the photoluminescence (PL) measurements at room temperature; i.e., a PL profile measurement and a PL topography (PL pattern observation). PL profile measurement reveals the macroscopic defect distribution, such as swirl defects. On the other hand, PL topography provides information about microscopic defects, e.g. dislocations and stacking faults. The correlation between the PL topograph and the defects are examined by preferential etching.

Catastrophic degradation of GaAlAs DH laser diodes

The catastrophic degradation of GaAlAs DH laser diodes is examined with the application of pulsed or dc current. The dependence of the pulsewidth on the degradation is measured using samples with or without facet coating. The light output PD at which the catastrophic degradation occurs decreases with an increase in the pulsewidth in the pulsewidth range 100 nsec to 10–50 μsec, and PD is constant over the pulsewidth of 10–50 μsec. The sample with an Al2O3 film coating has the highest PD. Photoluminescence patterns of the active layer in degraded samples both with and without facet coating show the growth of DLD’s in the 〈110〉 direction from the vicinity of a facet in the stripe region.

Photoluminescence topographic observation of defects in silicon crystals

A simple rapid nondestructive method of evaluating defects in silicon crystals is developed. This method is basically an observation of photoluminescence (PL) pattern or PL topography. The correlation between the PL topograph and the defects are examined by preferential etching. Stacking faults and dislocations which are known to adversely affect many devices are found to be observed as dark spots in the PL topograph.

Photoluminescence measurement of ion-etched GaAs surface

The effects of ion etching and annealing of GaAs were studied by observing photoluminescence, reflectance, and electron diffraction patterns. The (100) surfaces of GaAs were rf sputter etched. The intensity of the edge emission decreased to about 1/15 of the initial value in the case of a Si-doped sample when excited by a He–Cd laser (3250 Å) at 10 K. The depth of the damaged layer is deduced to exceed the bombarding ion range. Annealing increased the edge emission intensity up to the temperature of 450 °C, above which edge emission decreased due to thermal dissociation. On the other hand, electron diffraction patterns and reflection spectra showed continuous recovering of lattice ordering above the annealing temperature of 450 °C.

Measurement of minority carrier lifetime during gradual degradation of GaAs-Ga<inf>1-x</inf>Al<inf>x</inf>As double- heterostructure lasers

Minority carrier lifetime in the active layer of GaAs-Ga 1-x - Al x As double-heterostructure lasers has been found to decrease during gradual degradation by measuring the lasing delay time. This phenomenon is ascribed to a decrease in the internal quantum efficiency. Furthermore, a development of the inhomogeneity in the active layer is deduced from observations of the change of near-field patterns, light intensity versus current characteristics, and photoluminescence patterns.