Hisao Nakashima

Temperature dependence of stresses in chemical vapor deposited vitreous films

Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measured in situ from room temperature (RT) to 900u2009°C. As‐deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500u2009°C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900u2009°C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900u2009°C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500u2009°C can be represented as a function of phosphorous concentration in molu2009% P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties...

Degradation sources in GaAs-AlGaAs double-heterostructure lasers

Several sources of the dark-line defect (DLD) that causes rapid degradation of GaAs-AlGaAs double-heterostructure (DH) lasers have been identified by means of photoluminescence (PL) topography and a laser-induced degradation technique. All the sources that have been identified correspond to crystal defects, among which dark-spot defects (DSD) that are native to as-grown wafers are found to be most important. The growth and propagation processes of DLDs and DSDs have also been investigated. These defects are found to be highly mobile under high-intensity laser pumping. The correlation between the substrate dislocations and the DSDs has been examined by etching and X-ray topography. Although most DSDs correspond to etch-pits in epilayers, they are not always correlated with substrate dislocations.

Mesa-stripe-geometry double-heterostructure injection lasers

Fabrication and characteristics of mesa-stripe-geometry double-heterostructure injection lasers are described. Two types of lasers have been prepared: 1) low mesa-type lasers in which mesa etching is stopped just above the active layer and 2) high mesa-type lasers in which mesa etching is effected up to the first epitaxial layer (n-GaAlAs). The stripe widths of these lasers can be narrowed below 30 μm without an appreciable increase of the threshold current density. As a result, very low current operation has been realized. The thermal resistances of these lasers are nearly as low as those of stripe-geometry lasers. This property along with the low threshold current density renders it easy to operate diodes continuously at and above room temperature. Near-single-mode operation has been observed in low mesa-type lasers. The laser emissions display TE polarization in most cases; however, diodes with thick active layers have often been observed to show TM polarization.

Dark‐line defects induced by mechanical bending in GaAs‐Ga1−xAlxAs double‐heterostructure wafers

A 〈110〉‐oriented dark‐line defect (DLD) has been induced by mechanical bending in GaAs1−xAlxAs double‐heterostructure (DH) wafers. Both the concave upward and the convex upward bending (with the DH epitaxial layer as the upward surface) of the DH wafer has been carried out using a four‐point bending technique. The DLD formation has shown both the stress‐direction dependence and the asymmetry of the DH wafer. Photoluminescence topography has shown that the characteristics of the DLD’s are exactly the same as those of the optically induced DLD’s. From experimental results, it is conjectured that a glide‐multiplication mechanism is probably acceptable for the production of the 〈110〉 DLD dislocations.

Device characteristics of GaAlAs buried-multiquantum-well lasers fabricated by Zn-diffusion-induced disordering

A new transverse mode controlled buried-multiquantum-well (BMQW) laser has been fabricated using the simple and reliable Zn-diffusion-induced disordering process. BMQW lasers are characterized by low threshold current (20 mA) and single transverse and longitudinal mode oscillation. It is observed that the threshold current is proportional to the stripe width and the transverse mode is controlled by controlling the stripe width. From these results, it is confirmed that the BMQW structure provides good optical confinement as well as current confinement.

X‐ray topographic study of dark‐spot defects in GaAs‐Ga1−xAlxAs double‐heterostructure wafers

Dark‐spot defects (DSD) in a GaAs‐Ga1−xAlxAs double‐heterostructure (DH) wafer are studied by x‐ray topography. Such DSD’s are one of the primary sources of the dark‐line defects (DLD) that cause rapid degradation of GaAs‐Ga1−xAlxAs DH lasers. By using x‐ray topography almost all DSD’s observed by photoluminescence topography are correlated with dislocations in a GaAs substrate. In addition, it is observed that some dislocations in the substrate are not sources of DSD’s when the dislocation axes are nearly parallel to the surface of the substrate.

Photoluminescence study of laser annealing in phosphorus‐implanted and unimplanted silicon

Photoluminescence (PL) measurements are used to study the effects of laser annealing on phosphorus‐implanted and unimplanted silicon. PL measurements give a higher threshold energy for annealing than do electrical measurements. Dependence of crystal‐quality recovery on dose and laser‐annealing energy are examined. The PL intensity of the laser‐annealed high‐dose (8×1015 cm−2) sample is comparable to that of bulk silicon. On the other hand, laser annealing reduces the PL intensity of unimplanted silicon. These annealing effects are explained in terms of the temperature rise at the sample surface during annealing. In addition, laser annealing of vacuum‐deposited amorphous‐silicon layers leads to the growth of epitaxial layers with PL intensities as high as bulk silicon.

Growth and propagation mechanism of 〈110〉‐oriented dark‐line defects in GaAs‐Ga1−xAlxAs double heterostructure crystals

Application of external stress on a double heterostructure (DH) crystal is used to induce 〈110〉‐oriented dark‐line defects (DLD). The stress is applied by using a four‐point mechanical bending apparatus. Resulting DLD formation is found to depend on stress direction and DH crystal orientation. This asymmetric DLD introduction can be explained by the difference in glide motion between α and β dislocations. It is shown that a threshold stress exists for the DLD formation. This threshold stress and the growth velocity of the DLD’s strongly depend on optical pump intensity. Extension of the DLD’s into the ternary passive layers is observed by x‐ray topography and phase‐contrast microscopy. This observation suggests that stresses caused by local heating at the site of a defect play an important role in inducing 〈110〉 DLD’s. These experimental results lead to the conclusion that dislocation glide processes are responsible for 〈110〉‐DLD propagation.

Photoluminescence observation of swirl defects and gettering effects in silicon at room temperature

Swirl defects are nondestructively observed in silicon using a photoluminescence profile taken at room temperature. A precise geometrical correspondence between the photoluminescence profile and swirl pattern is obtained. High photoluminescence intensity spots correspond to low defect density regions and vice versa. The usefulness of this method for evaluating silicon crystals is also confirmed by observing the gettering effects in oxidized epitaxial wafers where the back surface is ground.

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.