Abram Jakubowicz

Room-Temperature, Electric Field-Induced Creation of Stable Devices in CulnSe2 Crystals.

Multiple-junction structures were formed, on a microscopic scale, at room temperature, by the application of a strong electric field across originally homogeneous crystals of the ternary chalcopyrite semiconductor CulnSe2. After removal of the electric field, the structures were examined with electron beam-induced current microscopy and their current-voltage characteristics were measured. Bipolar transistor action was observed, indicating that sharp bulk junctions can form in this way at low ambient temperatures. The devices are stable under normal (low-voltage) operating conditions. Possible causes for this effect, including electromigration and electric field-assisted defect reactions, are suggested.

Lattice disorder, facet heating and catastrophic optical mirror damage of AlGaAs quantum well lasers

Raman microprobe spectra from dry‐etched, coated (110) AlGaAs single quantum well laser mirrors show, apart from the allowed phonon modes, a series of symmetry forbidden modes whose strength is dependent on the mirror treatment prior to coating. A particularly strong mode at 193 cm−1 can be attributed to disorder activated longitudinal acoustic phonon scattering in addition to—and this is new—the Eg‐mode of elemental arsenic. The existence of lattice disorder and arsenic clusters is confirmed by Rayleigh scattering and energy dispersive x‐ray spectroscopy. The optical power level at catastrophic optical mirror damage and the local mirror temperatures of the biased laser are found to have a strong dependence on mirror disorder.

Laser operation‐induced migration of beryllium at mirrors of GaAs/AlGaAs laser diodes

Laser operation‐induced migration of beryllium at laser mirrors was studied by electron‐beam‐induced current. The devices investigated were single quantum well graded index separate confinement GaAs/AlGaAs ridge geometry laser diodes. In these devices, an operation‐induced displacement of the p‐n junction towards the n‐type cladding has been observed close to the mirrors. A similar effect was induced by electron irradiation of the mirror facets in a scanning electron microscope. These effects have been attributed to recombination‐enhanced diffusion/migration of beryllium from the p‐type cladding. We have measured the diffusion coefficient of beryllium and, from this value, have estimated the average mirror temperature during laser operation. This temperature was found to be in excellent agreement with recently published measured mirror temperatures.

Revealing process‐induced strain fields in GaAs/AlGaAs lasers via electron irradiation in a scanning electron microscope

An electron beam induced current study has been performed on single quantum well graded index separate confinement heterostructure GaAs/AlGaAs ridge geometry lasers. It has been shown that electron irradiation in the keV range combined with the electron beam induced current technique can be used to reveal process‐induced strain fields and to study strain‐related degradation phenomena in these devices on a microscopic scale. This technique has revealed a strain field below the ridge and below an opening in the metal layer. Enhanced susceptibility to degradation processes has been detected close to the lower corners of the ridge. It is shown that a correct interpretation of electron beam induced current images requires, including as contrast mechanism, local fluctuations in the distribution of the electric potential in the device and capture properties of quantum wells; (in the past, electron beam induced current images of degraded lasers were interpreted under the assumption that the contrast reflects the ...

Aggregate structure in CuBSe2/Mo films (B=In,Ga): Its relation to their electrical activity

CuBSe2/Mo films of about 3 μm in thickness prepared on different substrates (Si single crystal, glass, alumina) by three‐source evaporation have been investigated by electron and optical microscopic techniques: Scanning electron microscopy [including (EBIC) electron‐beam‐induced current mode], conventional transmission electron microscopy (TEM), and optical Nomarski microscopy. They show, on top of their well‐known dense polycrystalline structure (≊1 μm average grain size), a more coarse ‘‘aggregate’’ structure with aggregate dimensions of 20–100 μm, depending on the substrate used. The aggregate boundaries are characterized by very poor EBIC collection efficiency. For samples on glass substrates, this structure, as detected in EBIC, correlates with deformation patterns of the Mo layer seen by Nomarski contrast when viewed through the glass side of the samples. Local electrical measurements made on small Schottky contacts reveal a correlation between the aggregate structure and the I‐V characteristics. TE...

Operational stability of 980-nm pump lasers at 200 mW and above

The understanding of failure mechanisms in InGaAs/AlGaAs 980 nm pump lasers has gained significantly in the last couple of years. Random failure reduction has been observed as a result of improved facet-passivation techniques, and improved packaging and chip technology. With todays wear-out extrapolation data and random-failure activation estimates, there is clearly outlook for operation at higher output- power levels (200 - 250 mW) than used so far at reasonably low random-failure rates and low failure-rate operation at lower power levels (e.g. 60 mW, 25 degree(s)C, towards 25 FIT?), which clearly stimulates the interest for application of 980 nm pumps in submarine applications.

Electronic effects of ion mobility in semiconductors: Mixed electronic–ionic behavior and device creation in Si:Li

Micrometer‐sized homojunction structures can be formed by applying strong electric pulses, at ambient temperatures, to Li‐doped, floating zone n‐Si. Two such junctions, arranged back to back, act as a transistor, as evidenced by electron‐beam‐induced current and current–voltage measurements. The structures are created during a time ranging from ∼100 ms to a few seconds, depending on the size of the structure. The phenomenon is similar to what was observed earlier in CuInSe2 and was explained there by thermally assisted electromigration of Cu. In the case of Si doped with Li we can use secondary‐ion‐mass spectrometry to detect the redistribution of Li after electric‐field application. Such a redistribution is indeed found and corresponds to an n+‐p‐n structure with the p region extending at least ∼20 μm into the bulk of Si. Structures created in Si doped with Li in this way are stable for at least 13 months after their creation. We ascribe this to the large difference between Li diffusivity at the local te...

The effect of pressure on the band-gap energy in ordered GaInP and AlGaInP grown by MOVPE

Abstract Photoluminescence (PL) measurements on Ga 0.52 In 0.48 P and Al 0.18 Ga 0.34 In 0.48 , P alloys, grown by metalorganic vapor phase epitaxy (MOVPE) on GaAs, have been made as a function of pressure up to about 4.5 GPa at 77 K. The substrates are oriented on the (100) and off the (100) plane toward [011] and [011] by up to 25 °. The band-gap energy anomaly in the CuPt-type ordered structure has been systematically investigated at high pressures. With increasing pressure the E 0 band gap shows a sublinear shift toward higher energies. For some samples, this shift tends to saturate, of the PL peak shows a decrease in energy with pressure. The pressures needed for these observations are found to be significantly smaller in AlGaInP than in GaInP. The observed behaviors strongly depend on substrate misorientation, and hence reflect the degree of ordering in these alloys. These results clearly demonstrate the importance of the effects of repulsion between the Γ-folded energy states on the optical spectra in the CuPt-type ordered structure. Possible explanations for some of the trends in high-pressure behavior of the E 0 direct band gap in GaInP and AlGaInP samples having different degrees of ordering are discussed, including the modification of the ordinary Γ-X crossover upon ordering.

Effects of chemical and electrochemical etching on polycrystalline thin films of CuGaSe 2

Electrochemical and, especially, chemical oxidative etching drastically improves the photoresponse of liquid electrolyte/CuGaSe2-on-Mo junctions. This is expressed in decreased effective doping levels and increased effective minority carrier diffusion lengths. It is accounted for by removal of highly defective surface layers, which also leads to an increase in the barrier height, as judged from a positive shift of the flat band potential (on the electrochemical scale). The etching effects are seen clearly in Zn/CuGaSe2 devices, by electron beam-induced current. This last method also reveals a supra-grain structure, which is tentatively explained by thermal stress-induced strain at the Mo-CuGaSe2 interface.

Electron beam charging thermography of mirrors of semiconductor laser diodes

Charging insulating films in a scanning electron microscope is shown to be a potentially useful thermographic technique which makes it possible to reveal hot regions in microelectronic devices, with a spatial resolution in the submicrometer range. This technique entails depositing an insulating film on the device to serve as thermographic medium. A focused, low‐energy electron beam charges the insulator during the scanning process. Hot regions modify the local charge, which in turn modifies the secondary electron signal and thus generates a thermal contrast. This technique has been applied to investigate mirrors of GaAs/AlGaAs graded index separate confinement single quantum well laser diodes. Thermographic images of these mirrors have been obtained with a spatial resolution of 0.25 μm. Since the thermal images can be observed using the scanning electron microscope’s TV mode, the course of fast thermal phenomena at laser mirrors can be imaged. As an example, the thermal drift prior to the thermal runaway ...