Nobuyuki Ikoma

Metalorganic Vapor Phase Epitaxial Growth of GaNAs Using Tertiarybutylarsine (TBA) and Dimethylhydrazine (DMHy).

GaNAs alloys were successfully grown on GaAs substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE) with all organometallic sources of triethylgallium (TEG), tertiarybutylarsine (TBA), and dimethylhydrazine (DMHy). For nitrogen, the desorption coefficient of 30 kcal/mol was derived from the nitrogen incorporation dependence on growth temperature. Since the nitrogen concentration above 3% was easily achieved by our growth technique, the combination of TBA-DMHy as V precursors is a candidate for the growth of other III-V alloys containing nitrogen. We observed a decrease in PL intensity with enhancing nitrogen incorporation into solids. In order to recover from degradation of optical properties, rapid thermal annealing (RTA) was demonstrated and found to be effective. Therefore MOVPE using TBA-DMHy combined with postgrowth annealing is expected to obtain GaNAs alloys with high nitrogen concentration as well as excellent optical properties.

InAs Island Formation Aligned along the Steps on a GaAs(001) Vicinal Surface

InAs island formation on a GaAs(001) substrate misoriented by 1° toward the [110] direction was investigated by scanning tunneling microscopy. On a 2.0ML InAs-deposited GaAs surface, three-dimensional islands were observed; some of the islands were aligned along the [10] direction. That is, the islands were selectively formed at steps running relatively straight along the [10] direction on the GaAs surface. These results show the possibility of controlling the arrangement of InAs islands on a surface by controlling the step structure on the surface, which induces selective island formation at the steps.

Role of Steps in GaAs Heteroepitaxial Growth on InAs(001) Surfaces.

The role of steps during the initial stages of GaAs growth on InAs surfaces was investigated by scanning tunneling microscopy (STM). The surface structures of a nominally (001) InAs substrate and a misoriented (001) InAs substrate tilted by 1° towards the [111]B direction were observed by STM after a certain amount of GaAs deposition. In the case of a nominally (001) surface, a growth mode transition from two-dimensional (2D) to 3D island growth occurred when more than 0.75 ML GaAs was deposited. On the other hand, in the case of a vicinal surface, a growth mode transition did not occur when the same amount of GaAs was deposited onto the surface. In this case, GaAs-selective growth attached to the step edges and crack formation extending in the [10] direction were observed in the STM images. These results indicate that the initial growth stages of GaAs heteroepitaxy on an InAs vicinal surface are different from those on a nominally (001) InAs surface due to the existence of steps.

Surface structures of InP and InAs thermally cleaned in an arsenic flux

The surface structures of InP and InAs thermally cleaned in an arsenic flux were investigated using an ultrahigh vacuum scanning tunneling microscope multichamber system equipped with a molecular beam epitaxy facility. The InP surfaces thus treated at 510 °C showed In‐stabilized (4×2) reconstructions which depended on the time of thermal cleaning. The surface structure of this substrate after thermal cleaning for 3 min comprised one In dimer and three missing dimers. This structure was the same as that of InAs treated under the same conditions. These In‐stabilized (4×2) structures formed on both InP and InAs substrates changed to an As‐stabilized (2×4) structure when the substrate temperature was lowered to below 480 °C under the same arsenic pressure.

Surface Treatment by Ar Plasma Irradiation in Electron Cyclotron Resonance Chemical Vapor Deposition

To reduce the surface states of GaAs and related semiconductors which originate from native oxides on a surface, we developed a simple surface treatment method in which the surface oxides could be physically sputtered by Ar plasma irradiation in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) apparatus. In the experiment of Ar irradiation of a GaAs surface, we were able to determine the optimum irradiation time at which the native-oxide-related surface states were almost removed without damaging the irradiated surface. Then, we applied this method to an actual 0.98-µm semiconductor laser in which catastrophic optical damage (COD) failure occurred due to the surface states of the output facet. By irradiating Ar plasma to the output facet of the laser and removing the oxide-related surface states there, tolerance to COD was remarkably improved compared with that of a conventional non-Ar-irradiated one.

Highly reliable AlGaInAs buried heterostructure lasers for uncooled 10 Gb/s direct modulation

High reliability (estimated median lifetime of 240,000 hours) of 1.3 /spl mu/m AlGaInAs buried heterostructure lasers has been demonstrated by more than 10,000 hours accelerated aging tests. Distributed-feedback lasers have successfully operated at 10 Gb/s at 95/spl deg/C.

Step Structures on Vicinal InAs (001) under (2×4) and (4×2) Surface Reconstructions

Step structures on InAs (001) vicinal surfaces under two different surface reconstructions were investigated by scanning tunneling microscopy. On an InAs surface misoriented by 1° toward the [110] direction, relatively straight monolayer steps along the [10] direction were observed under an As-stabilized (2×4) reconstruction. On the other hand, step-bunching of about 10 monolayers was detected under an In-stabilized (4×2) reconstruction. On an InAs surface misoriented by 1° toward the [10] direction, ragged monolayer steps roughly running parallel to the [110] direction were seen under the (2×4) reconstruction. However, relatively straight steps along the [110] direction with step-bunching of 2-3 monolayers were observed under the (4×2) reconstruction. These results indicate that thermodynamically favorable step structures are different between the (2×4) and (4×2) reconstructions.

Scanning tunneling microscopy of argon‐ion bombarded GaAs (001) surfaces

The atomic structures of argon‐ion bombarded GaAs (001) surfaces were investigated using in situ scanning tunneling microscopy (STM). The experiments were conducted in an ultrahigh vacuum multichamber system equipped with a STM, a molecular beam epitaxy facility, as well as an argon‐ion gun. MBE‐grown GaAs surfaces were bombarded by argon ions of 500 eV at doses of ∼1013 ions cm−2, and the resulting surface structures were examined by a STM. In the STM images, most of the defects produced by the argon‐ion bombardment were about 1.6 nm wide in the [110] direction. This result seems to suggest that the interaction of surfaces with argon ions during the bombardment took place in a (2×4) unit cell; that is, all of the three arsenic dimers of a (2×4) unit cell in the bombarded regions were taken away as if they comprised a single unit of interaction. The average defect density increased with increasing argon‐ion dose.

Electrostatic-discharge-induced degradation of 1.3μm AlGaInAs∕InP buried heterostructure laser diodes

Degradation of 1.3μm AlGaInAs buried heterostructure laser diodes due to electrostatic discharge (ESD) is studied. The degradation mechanism of this material has not previously been clear and so the ESD tolerance was evaluated. Degradation occurred at 0.5 and 2.5kV for forward and reverse polarities, respectively. Because that ESD tolerance for forward polarity is insufficient for practical applications, we focused on it in analyzing the degradation mechanism. Elliptically shaped melted regions are observed in the active layer of the facet. Such regions developed inside a cavity under the application of ESD pulses. These results indicate that degradation is caused by melting due to optical absorption.

MOVPE growth of GaNAs using tertiarybutylarsine (TBA) and dimethylhydrazine (DMHy)

GaNAs alloys were successfully grown on GaAs substrates by low-pressure MOVPE with all organometallic sources of triethylgallium (TEG), tertiarybutylarsine (TBA), and dimethylhydrazine (DMHy). We studied the incorporation behavior of nitrogen in terms of growth temperature and molar flow ratio of supplied sources. A ratio of TBA to the group III element, As/III, as low as 1.4 was found to be possible to grow GaNAs with good crystalline quality. Since the nitrogen concentration of more than 3% was easily achieved by our growth technique. The combination of TBA-DMHy as V precursors is a candidate for the growth of other III-V alloys containing nitrogen. We observed a decrease in PL intensity with enhancing nitrogen incorporation into solids: lowering growth temperature and increasing the fractional flow ratio of DMHy. In order to recover from degradation in optical properties, Rapid Thermal Annealing (RTA) was demonstrated and found to be effective. Therefore MOVPE using TBA-DMHy combined with post-annealing is expected to obtain GaNAs alloys with high nitrogen concentration as well as excellent optical properties.