Katsutoshi Sakakibara

Zn Diffusion into InP Using Dimethylzinc as a Zn Source

A new method of Zn diffusion into InP using dimethyl-zinc(DMZ) as a Zn source is described. This diffusion method provides precise control over both diffusion depth and Zn concentration, and is easier to use and gives highly reproducible results. Diffusions were carried out from 400 to 570°C with the Zn surface concentration of 1017 to 1018 cm-3, and diffusion depth of 0.2 to 2 µm. The diffusion profiles were measured by SIMS analysis and electrolytic etching with simultaneous C-V measurement.

Incorporation of Arsenic and Gallium in InP Layers in GaInAs/InP Heterostructures Grown by MOVPE

The effects of arsenic (As) and gallium (Ga) incorporation in InP layers in GaInAs/InP heterostructures grown by low-pressure metal-organic vapor phase epitaxy (LP-MOVPE) on lattice parameter and band-gap energy of InP layers were studied. It was found that As and Ga incorporation is prolonged during InP growth after arsine (AsH3) and triethylgallium (TEG) flows are turned off, resulting in a lowering of the band gap energy and change in the lattice parameter of the InP layers. This incorporation is considered to originate from both desorption and diffusion of their outgassing sources produced during the growth of a thick GaInAs layer.

Diffusion of zinc acceptors in InAsP by the metal-organic vapor-phase diffusion technique

Diffusion of zinc acceptors in InAsP by a metal-organic vapor-phase diffusion technique, whereby a low-pressure metal-organic vapor-phase epitaxy with dimethylzinc and phosphine is utilized as an open tube diffusion system, is demonstrated to accurately control the diffusion depth in the submicrometer range. The annealing effect on the zinc diffusion profiles in InAsP was found to be the activation of zinc acceptors similar to that in InP, but the maximum hole concentration of 1×1019 cm−3 for the zinc diffusion in InAsP was achieved.

GaInAs/InP PIN Photodiodes Fabricated by MOVPE and a New Zn Diffusion Technique

GaInAs/InP photodiodes were fabricated by selective zinc diffusion using dimethylzinc as a zinc source to form the p+-region and selective p+-GaInAs growth to produce good ohmic contacts using low-pressure MOVPE. These photodiodes have an external quantum efficiency of 60–80% in the 0.95–1.55 µm-wave-length range, and a dark current of about 30 pA at -2 V and a -3 dB cutoff frequency of 1.4 GHz at 0 V were measured for 110 µm-diam diodes. These results show that this diffusion method is a useful process for fabricating photodiodes or other optical devices.

Evaluation of Surface Zn Concentration in Zn Diffusion into InP

The surface Zn concentration of Zn diffusion in InP was evaluated with a simple model using statistical thermodynamics, assuming that the Zn atoms in the vapor phase are isolated atoms of monoatomic gas and that the interaction between the incorporated Zn atoms in InP is negligible. The results confirmed that the surface Zn concentration obtained from diffusion experiments is well described in terms of this model. Thus, this analysis strongly supports the fact that Zn atoms are incorporated in InP not only as singly ionized acceptors, but also as singly ionized donors.

Effects of Phosphorus Pressure on Low-Energy Emission Bands in Zn-Diffused InP

The effects of phosphorus pressure during Zn diffusion and sequential annealing on the diffusion profiles and the photoluminescence spectra were investigated by secondary ion mass spectrometry (SIMS) analysis, capacitance-voltage (C-V) and photoluminescence (PL) measurements. Zn diffusion was performed using dimethylzinc as the Zn source. We found that as the PH3 flow rate increased, the diffusion depth deepened and a low-energy broad emission band at 1.23-1.32 eV (77 K) from near the Zn-diffused surface shifted to higher energy while its intensity increased. Another low-energy emission band at 1.28-1.33 eV (77 K) was observed in the Zn-diffused InP with high Zn interstitial concentration. The excitation and temperature dependences of the peak energies indicate that these bands are the so-called quasi-donor-acceptor pair bands with lattice relaxation. These results, along with the effect of annealing, suggest that a Zn incorporation mechanism with a contribution from phosphorus-related defects occurs near the surface.

Wide-Wavelength GaInAs PIN Photodiodes Using a Lattice-Mismatched Light-Absorbing Layer and a Thin InP Cap Layer

We have fabricated PIN photodiodes (PDs) with a thick lattice-mismatched GaInAs absorbing layer and a thin InP cap layer by metal-organic vapor phase epitaxy (MOVPE). The lattice mismatch and the X-ray FWHM of 2.3-µm GaInAs were 0.5% and 138 arcsec, respectively. These PDs exhibited a very low temperature-dependent response from 1.0 to 1.70 µm with quantum efficiencies as high as 45% at 0.78 µm, 86% at 1.3 µm, 85% at 1.55 µm and 70% at 1.75 µm. A reverse leakage current of 30 nA at -2 V bias was measured, and a -3 dB cutoff frequency of 2.5 GHz was obtained for the 110 µm-dia. PDs.

Photoluminescence and Photoemission Studies of Defects in InP Induced by Zn Diffusion

Defects in InP induced by Zn diffusion have been studied by measuring the photoluminescence and photoemission spectra in Zn-diffused samples fabricated using our new diffusion technique. Results indicate that Zn diffusion generated broad emission bands in the energy range of 0.7-1 eV only in the surface layer with a thickness of less than about 100 nm and left a P-rich layer with a very high Zn concentration and a thickness of less than about 20 nm. It is suggested that Zn diffusion with a high Zn-concentration source under P-rich conditions occurs near the surface and induces deep centers responsible for these bands.

High-Speed GaInAs PIN Photodiodes with Low Series Resistance

We have demonstrated high-speed GaInAs PIN photodiodes fabricated by low-pressure metalorganic vapor-phase epitaxy. To reduce series resistance, a heavily sulfur-doped InP layer and graded band-gap (GaxIn1-xAs x=0.47 to 0) contact layer were incorporated into the photodiodes. Furthermore, to reduce stray capacitance, a semi-insulated substrate was used and mesa islands were passivated with polyimide. As a result, the RC time constant then decreased and a bandwidth of 31 GHz at 1.54 µm was obtained for a 160-mm2 junction-area diode. The series resistance for the diode with an electrode area of 24 µm2 was 47 Ω, estimated by fitting measured current-voltage curves. These results show that these layers are useful for reducing the series resistance of high-speed GaInAs photodiodes.