T. Kimura

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.

Long-Wavelength Receiver Optoelectronic Integrated Circuit on 3-Inch-Diameter GaAs Substrate Grown by InP-on-GaAs Heteroepitaxy.

A monolithic long-wavelength receiver optoelectronic integrated circuit (OEIC), which integrates an InGaAs PIN-photodiode (PD) and a GaAs field-effect transistor (FET), has been successfully fabricated on a 3-inch-diameter GaAs substrate using InP-on-GaAs heteroepitaxy, by metalorganic chemical vapor deposition (MOCVD) and conventional GaAs-IC process technology. The epitaxial quality of the PD layer has been improved by use of a low-temperature-grown buffer layer, thermal cyclic annealing and an InGaAs/InP strained-layer superlattice. The integrated PD has low dark current of 10 nA at -5 V bias voltage, and exhibited stable operation at 175°C. The fabricated receiver OEIC has 1.4 GHz bandwidth and sensitivity of -28.1 dBm at the transmission rate of 622 Mb/s with bit error rate of 10-9, which is applicable to practical subscriber optical communication systems.

Dark current and diffusion length in InGaAs photodiodes grown on GaAs substrates

In0.53Ga0.47As photodiodes grown on GaAs substrates have been fabricated and analyzed. The dislocation density in the InGaAs layer is 2×107 cm−2. A lowest dark current of 3.8×10−4 A/cm2 at 10 V bias is obtained, which is very stable during a bias‐temperature test of Vb=−10 V, T=175u2009°C, and t=100 h. The quantum efficiency is more than 85% at λ=1.3 μm. This device is expected to be practically used. The dark current has been successfully explained by the thermionic emission and thermionic field emission from traps at midgap. The diffusion length of holes in the InGaAs layer is explained by the recombination at dislocations with the finite recombination velocity of S∼104 cm/s.

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.

Analysis of the in-plane bandgap distribution in selectively grown InGaAs/InGaAsP multiple quantum well by low pressure metalorganic chemical vapor deposition

Abstract The in-plane distribution of growth rate enhancement and bandgap ( E g ) of the selectively grown InGaAs/In GaAsP multiple quantum well (MQW) structure using a twin stripe mask is investigated. The dependence of the growth rate enhancement and E g transition profile on the mask widthand mask opening width is investigated experimentally, and discussed by the simulation based on the vapor phase diffusion model of the re-evaporated reactant from the mask to the open area. Growth profile in the direction perpendicular to the stripe is explained by one-dimensional vapor phase diffusion. Bandgap transition length along the mask opening stripe decreases with decreasing the mask width and the mask opening width. In-plane bandgap distribution is calculated by simple two-dimensional diffusion model, and the results are consistent with the experimental data.

Extremely low threshold InGaAsP/InP DFB laser by MOCVD/LPE hybrid process

Abstract The InP and InGaAsP layers grown by low pressure MOCVD were characterized by a double crystal X-ray diffractometry and 4.2 K photoluminescence measurements. It was confirmed that these layers were of high quality and the hetero-interfaces were very sharp. The growth characteristics on corrugated substrates were investigated for the application to 1.3 μm InGaAsP/InP distributed feedback (DFB) laser diodes. These devices exhibited extremely low threshold currents of 3.8 mA in CW mode at 20 ° C for a normal cavity length of 300 μm. The typical values of the differential efficiency (η) and the characteristic temperature ( T o ) were 0.25 mW/mA and 53 K, respectively. Single longitudinal mode operation was attained up to 25 mW light output. These results show a great potential of MOCVD for the fabrication of InGaAsP/InP optical devices.

Metalorganic vapor-phase epitaxial regrowth of InP on reactive ion-etched mesa structures for p-substrate buried heterostructure laser application

Growth behavior of sulfur-doped n-InP around reactive ion-etched (RIE) mesas has been investigated for realization of p-substrate buried heterostructure laser utilizing metalorganic vapor phase epitaxy. It is found that the growth of n-InP layer on the sidewall of the mesa ((1 1 0) plane) is significantly suppressed, as the flow rate of hydrogen sulfide (H2S) which is used for n-type doping, increased. This phenomenon of growth suppression was also observed for growth of highly S-doped n-InP on narrow (0 0 1) facets. Taking account of both, these phenomena can be explained by migration enhancement of indium atoms on sulfur-terminated surfaces caused by excess H2S supply. Consequently, the shape of the regrown embedding layer was found to be exactly controlled by the H2S flow rate. Using this technique, a p-substrate 1.3 μm buried heterostructure laser with pnp current-blocking structure has been successfully fabricated around the RIE mesa and excellent lasing characteristics with high reliability has been realized for the first time.

Threshold current density dependence on p-doping in AlGaInP laser

Minimum threshold current density (Jth) less than 2.OkA/cm2 is obtained at optimum hole concentration in the Zn-doped cladding layer (NH) of 34x 1O7ca3 in the AlGaInP laser diodes. At NM lower than optimum one, Jth increases gradually due to poor electron confinement in the active layer. At NH higher than optimum one, Jth also increases due to Zn diffusion from the Zn-doped cladding layer to the active layer during epitaxial growth. One of the reasons is that Zn atoms act as nonradiative recombination centers in the active layer. By optimizing NH in the index guide AlGaInP laser diodes with 6u a width stripe, threshold current of 4OmA and astigmatism smaller than 8 m are achieved.

Improved selective growth of InP around dry-etched mesas by metalorganic chemical vapor deposition at low growth temperature

A comparative study has been carried out regarding selective embedding growth of InP by metalorganic chemical vapor deposition (MOCVD) around dry-etched mesas, using two types of reactors: a conventional horizontal type and a highspeed rotating-susceptor type. In the case of the conventional horizontal-type MOCVD, overgrowth on the mask was observed when the growth temperature was low (600°C). On the other hand, an almost planar grown surface without such overgrowth was achieved by using the high-speed rotating-susceptor MOCVD for a wide range of growth temperatures, especially even at a low growth temperature of 580°C. Regarding the high-speed rotating-susceptor MOCVD, we have also investigated the effects of dopants on the growth behaviors and have found a remarkable difference between n-type S-doped and p-type Zn-doped InP in the growth behaviors. The mechanism for suppressing overgrowth in case of the high-speed rotating-susceptor MOCVD, as well as the cause for the different effects between the dopants, are discussed.

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.