M. Tsugami

Improvement of InP crystal quality grown on GaAs substrates and device applications

We have investigated the effect of strained-layer superlattice (SLS) buffer layers on the crystal quality of InP grown on GaAs substrates. The various SLSs such as In0.63Ga0.37As/InP, In0.73Ga0.27As/InP, In0.9Ga0.1P/InP, and GaAs/InP were tested. It is found that the optical property of InP layers grown on In0.63Ga0.37As/InP SLSs was dramatically improved. An InGaAsP/InP double heterostructure laser diode and an InGaAs PIN photodiode (PD) on InP/GaAs with an In0.63Ga0.37As/InP SLS have been fabricated. The CW threshold current of the laser at room temperature was as low as 31 mA, and the dark current of the PD was 30 nA at - 10 V.

Effectiveness of AlGaAs/GaAs superlattices in reducing dislocation density in GaAs on Si

Abstract The effectiveness in reducing the dislocation density in a GaAs layer on a Si substrate (GaAs-on-Si) is investigated by using AlGaAs/GaAs superlattices grown by metalorganic vapor phase epitaxy (MOVPE). The degree of dislocation density reduction is compared among several types of AlGaAs/GaAs superlattices with various layer thicknesses, various numbers of layers and various AlAs content of AlGaAs layer. The thicker each layer is, the larger the number of layers, or the larger the AlAs content, the larger is the degree of dislocation density reduction. As a result, the dislocation density is reduced to 1×10 6 cm −2 by using five periods of (20 nm Al 0.85 Ga 0.15 As)/(100 nm GaAs superlattice). The reduction of the dislocation density and the degree of this effect can be explained by the crystal hardening of AlGaAs and the bending of dislocations at the AlGaAs/GaAs superlattice.

Influence of oxygen on the threshold current of AlGaAs multiple quantum well lasers grown by metalorganic chemical vapor deposition

Abstract The influence of oxygen incorporation into the epitaxial layers on the threshold current density of AlGaAs multiple quantum well (MQW) lasers grown by metalorganic chemical vapor deposition (MOCVD) is studied quantitatively. It is shown that reduction of the oxygen concentration under 1X10 17 cm -3 in the cladding layers is necessary to obtain low threshold current density for the MQW lasers emitting at 780 nm. The effective carrier lifetime measurement in the active layer by time-resolved photoluminescence (PL) spectroscopy is a simple and effective method to monitor the oxygen contamination in the epitaxial layers.

Uniform Fabrication of Highly Reliable, 50-60 mW-Class, 685 nm, Window-Mirror Lasers for Optical Data Storage

Uniform fabrication of highly reliable 50–60 mW-class 685 nm laser diodes (LDs) with a window-mirror structure has been realized by using selective solid-phase Zn diffusion and three-inch full wafer processing. A window-mirror structure at the LD mirror is formed by Zn-induced disordering of an ordered GaInP multiple quantum-well (MQW) active layer. High uniformity of characteristics such as the operating current and the far-field pattern has been obtained by realization of highly uniform Zn diffusion. A small astigmatic distance (ΔZ3 µ m), a low relative intensity noise (RIN-135 dB/Hz) and a high speed response (T r, T f1.2 ns) are obtained in addition to the high-power and high-temperature characteristics (70 mW, 80° C) in spite of the existence of the window structure. The LDs have exhibited reliable 6,000–10,000 h operation under the conditions of 60° C and 50–60 mW for the first time.

Improvement of InP Crystal Quality on GaAs Substrates by Thermal Cyclic Annealing

We have studied the effect of thermal cyclic annealing (TCA) on the crystal quality improvement of MOCVD grown InP on GaAs substrates. The crystal quality has been evaluated by the etch pit density (EPD), X-ray diffraction and photoluminescence (PL) measurement. It is found that the TCA is effective in reducing the dislocation density, and that the annealing at 700°C is essential to confine the point defects near the InP/GaAs interface. The EPD is reduced from 6×107 cm-2 to 3×107 cm-2, and the defect-related PL peak intensity is decreased below the residual level in the 5 µm-thick InP on GaAs.

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.

Reliability study on 50-100-mW CW operation of 680-nm visible laser diodes with a window-mirror structure

We have studied reliability of 680-nm visible laser diodes (LDs) with a window-mirror structure formed by zinc-diffusion-induced disordering of GaInP quantum wells. Aging tests under the condition of CW output power in the range of 50-100 mW for ambient temperature from 40/spl deg/C to 70/spl deg/C have been carried out for 650-/spl mu/m-long LDs and 900-/spl mu/m-long LDs with three kinds of the front facet reflectivities (1.5%, 6% and 13%). In all tests, laser operation was stable for over 5000 h. For example, reliable 500-10000-h operation of the 900-/spl mu/m LDs was realized under the conditions of output power of 50 mW at 70/spl deg/C, 70 mW at 60/spl deg/C, and 100 mW at 40/spl deg/C for the first time. By various aging test results, dependence of the temperature and the output power on increase of the operating current has been investigated. Also, influences of the facet reflectivities and the cavity lengths on the reliability have been studied with focus on the optical power density and the current density. Consequently, it has been clarified that the degradation of the window LDs rather strongly depends on the operating current density than the optical power density. Moreover, it has been proven that the reliability of the window LDs is effectively improved by the reduction of the operating current density due to extension of the cavity length.

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

Zn diffusion mechanism in n-GaAs/Zn-AlGaAs/Se-AlGaAs structures

Abstract Zn diffusion has been investigated in n-GaAs/Zn-AlGaAs/Se-AlGaAs structures during growth of n-GaAs layers. Se and Si are used as dopants for the n-GaAs layer. Zn diffusion in these structures depends strongly on the kind of dopant as well as on the carrier concentration in the n-GaAs layer. The amount of Zn diffused into both n-GaAs and Se-AlGaAs layers is much smaller for the Si-doped GaAs layer than for the Se-doped one. The slower Zn diffusion during the growth of Si-doped GaAs layers in these structures is reasonably interpreted by modifying the model that interstitial Ga diffused from the n-GaAs layer into the Zn-AlGaAs layer kicks substitutional Zn out. The density of interstitial Ga in the Si-doped GaAs layer could be lower than in the Se-doped GaAs, because the interstitial Ga atoms replace Si occupying the column III site, while this is not the case for Se-doped GaAs where Se occupies the column V site.

Characteristics of 680 nm-visible laser diode with MQB grown by MOCVD

The authors introduced MQB (multiquantum barrier) structure grown by metal-organic chemical vapor deposition in an AlGaInP visible laser and improved the laser characteristics. The threshold current at 70 degrees C is reduced from 70 mA to 56 mA, and the characteristic temperature in the range over 70 degrees C is improved from 52 K to 69 K. This improvement is due to the suppression of carrier overflow by the MQB structure. This is a kind of electron wave interference device working at room temperature.<<ETX>>