Kaoru Kadoiwa

Effect of Employing Positions of Thermal Cyclic Annealing and Strained-Layer Superlattice on Defect Reduction in GaAs-on-Si

This paper describes the dependence of the dislocation density reduction effect on the employing position of either thermal cyclic annealing (TCA) or InGaAs-GaAs strained-layer superlattice (SLS) in GaAs-on-Si grown by metalorganic chemical vapor deposition (MOCVD). The dislocation density is reduced to one twenty-fifth of that in as-grown sample by the TCA as the position of TCA becomes farther than about 1.5 µm from the Si surface. The dislocation density is additionally reduced to one third by the SLS as the position of SLS becomes farther than about 2.0 µm. As a result, the dislocation density is reduced to 1.5 × 106 cm-2 by the combined use of TCA and SLS. The dislocation density reduction effect of TCA is determined mainly by the degree of residual stress. That effect of SLS is determined mainly by the degree of additional stress generated by SLS.

Mechanism of Zn passivation in AlGaInP layer grown by metalorganic chemical vapor deposition

Abstract The mechanism of passivation effect on the hole concentration in Zn-doped (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P layers grown by metalorganic chemical vapor deposition (MOCVD) is investigated. It is found that oxygen concentration in AlGaInP should be suppressed under 5 x 10 16 cm -3 in order to make the passivation behavior clear without effect of oxygen contamination, which was controlled by employing a high-grade gas purifier. The passivation of zinc acceptors has been effectively avoided by optimizing of the cooling atmosphere. The hole concentration increased with raising the AsH 3 flow stopping temperature after growth and it saturated at above 500°C. High hole concentration (beyond 1 x 10 18 cm -3 ) was achieved by combining the anti-passivation technique and the oxygen control techniques. We suggest from the hole concentration dependence on the measuring temperature that the new deep acceptor level due to the Zn passivation causes the hole concentration reduction in the AlGaInP layer.

The Multiple Quantum Barrier Structures and their Application to the High Power Visible Laser Diode with the Strained InGaP Active Layer Grown by MOCVD

Abstract We introduced a multiple quantum barrier (MQB) which was grown by MOCVD between the active layer and p-cladding layer to enhance potential barrier height. The MOCVD system was improved to realize the growth of MQB structures for the first time. We compared threshold current densities (Jth) of various barrier/well thickness combinations in order to optimize the MQB structure. We found that the thickness of barriers and wells should be 1.7 and 1.15 nm, respectively, to minimize Jth. The optimized MQB significantly reduced the Jth of visible laser diodes. Strained active layers with compressive stress were employed as another approach for the improvement of the threshold current. We found that the strained active layer is as effective as the MQB in reducing Jth. The lowest Jth has been achieved by the combination of MQBs and strained active layers. We realized an output power of 40 mW, at 90°C, at a lasing wavelength of 675 nm. to our knowledge, these are the best data.

GaAs(001) Epitaxial Layer on SOS Using a Specifically Designed MOCVD System

GaAs (001) single-domain and high-quality layers are obtained on slightly misoriented Si (001)-on-sapphire (012) substrates by using a new MOCVD system specifically designed for GaAs-on-Si growth. The X-ray FWHM of 10 µm-thick GaAs is reduced from 140 arcsec to 65 arcsec by thermal cycle annealing. A crack-free 15 µm-thick GaAs layer with a dislocation density of 3×106 cm-2 is obtained by combining the thermal cycle annealing and the strained-layer superlattices.

Surface morphology improvement of GaAs-on-Si using a two-reactor MOCVD system and an AlAs/GaAs low temperature buffer layer: an approach to crack-free GaAs-on-Si

Abstract Non-uniform thermal stress distributions due to surface defects can be the origin of crack formation for GaAs layers deposited on Si substrate. A two-reactor MOCVD system specifically designed for GaAs-on-Si has been successfully applied to reduce surface defects of GaAs layers on Si. Three different low temperature buffer layers (LTB) of GaAs, A1As and A1As/GaAs were examined in order to study further improvement effect on the surface morphology. An A1As/GaAs LTB was found to be the most effective for reducing the surface defects. The surface defect number in a GaAs layer on a 3 inch Si wafer is reduced from 1433 (GaAs LTB) to 488 by introducing the A1As/GaAs as a LTB. This resulted in crack-free material for GaAs thickness exceeding 5μm. The use of thermal cycle annealing and the InGaAs/GaAs strained layer superlattices (SLS) is also investigated.

Study of initial buffer layer in GaAs-on-Si growth

Abstract An AlAs/GaAs low temperature buffer-layer (LTB) has been found to be effective for reducing the density of pit-defects in the GaAs layer grown on Si, which are the origin of micro-cracks. SEM observation has indicated that the Si surface is covered more smoothly and more uniformly by the AlAs/GaAs LTB rather than by conventional GaAs LTB. Consequently, the pit-defect density was remarkably reduced by employing the AlAs/GaAs LTB and the micro-crack free GaAs-on-Si with a GaAs thickness of 5 μm has been obtained.

Crack-free and low dislocation density GaAs-on-Si grown by 2-reactor MOCVD system

Abstract A 2-reactor MOCVD system is effective to reduce the surface defect which is the trigger for the crack formation, that enables one to obtain a 7 μm thick and crack-free GaAs layer on a 3 inch Si substrate. The etch pit density of the GaAs layer on Si substrate is reduced to 5 × 10 5 cm −2 by the combination of thermal cycle annealing and 2 sets of strained-layer superlattice buffer layers. The minority carrier lifetime measured by time resolved photoluminescence is also studied. It is found that PL lifetime mapping is useful as a non-destructive dislocation evaluation method.

Multi-wafer growth of highly uniform and high-quality AlGaInP/GaInP structure using high-speed rotating disk metalorganic chemical vapor deposition

Multi-wafer growth of highly uniform and high-quality AlGaInP/GaInP using a high-speed rotating disk metalorganic chemical vapor deposition (MOCVD) has been successfully realized by suppressing In desorption and oxygen contamination at high growth temperature around 700°C. The suppression of In desorption during high-temperature growth is achieved by an increase of the effective gas flow rate resulting from increasing disk rotational speed and reducing growth pressure. The layer thickness uniformity of both undoped GaInP and Zn-doped (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P layers is controlled within ± 5% over a 3-inch diameter wafer. The composition uniformity of undoped GaInP layer estimated form X-ray rocking curve is controlled within ± 2% over the 3-inch diameter wafer. The oxygen concentration in the (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P layers is substantially reduced to below 2 × 10 16 cm −3 . Excellent performance, uniformity and reliability of AlGaInP/GaInP double quantum well laser diodes are also obtained from the 3-inch diameter wafer prepared by multi-wafer growth

Crack propagation and mechanical fracture in GaAs-on-Si

This paper describes the study of crack propagation and mechanical fracture in GaAs-on-Si, which are closely related with the residual stress. The crack propagation is often observed as the GaAs thickness exceeds about 3 µm, and the upper limit of the number of cracks increases linearly as the GaAs thickness increases. The cracks propagate from the surface defects, where stress ten times larger than the original residual thermal stress in GaAs-on-Si exists. The mechanical fracture strength (ζ) of the GaAs-on-Si wafer decreases as the GaAs thickness increases, and becomes equal to that of the bulk GaAs at the thickness of about 3 µm due to the concentrated stress near the cracks. The back coating of SiO2 is effective for stress relaxation, and the preliminary result of about 3×108 dyn/cm2 of stress relaxation is obtained.

Reliability study on high power 638-nm triple emitter broad area laser diode

Reliabilities of the 638-nm triple emitter broad area laser diode (BA-LD) with the window-mirror structure were studied. Methodology to estimate mean time to failure (MTTF) due to catastrophic optical mirror degradation (COMD) in reasonable aging duration was newly proposed. Power at which the LD failed due to COMD (PCOMD) was measured for the aged LDs under the several aging conditions. It was revealed that the PCOMD was proportional to logarithm of aging duration, and MTTF due to COMD (MTTF(COMD)) could be estimated by using this relation. MTTF(COMD) estimated by the methodology with the aging duration of approximately 2,000 hours was consistent with that estimated by the long term aging. By using this methodology, the MTTF of the BA-LD was estimated exceeding 100,000 hours under the output of 2.5 W, duty cycles of 30% .