Saburo Takamiya

Thermal stability of AlInAs/GaInAs/InP heterostructures

The origin of the thermal instability of the AlInAs/GaInAs system is identified and a novel method to recover the thermal degradation is also demonstrated. The thermal diffusion of fluorine into the Si‐doped AlInAs layer is found to be the main cause of the electrical deterioration of this system. This finding has led to a method to recover the thermal degradation by purging the fluorine off using the reannealing in the ultrahigh‐vacuum condition. This method is now potentially becoming a good candidate as a tip for the AlInAs/GaInAs devices fabrication including laser diode and high electron mobility transistor.

Overview of recent development of HEMTs in the mm-wave range

Abstract Recent expansion in the demand for high frequency applications requires new transistors with better performance than the MESFETs, especially in the upper-microwave and mm-wave frequency ranges. To realize better transistors than the MESFET by utilizing features of the heterostructure, high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) are being developed. GaAs pseudomorphic HEMTs (PHEMTs) are currently the main type of low noise transistors being used in various microwave and mm-wave systems. Very low noise figures of 1.5 dB at 60 GHz and 2.1 dB at 94 GHz are achieved with GaAs PHEMTs. Furthermore, InP HEMTs, with better noise performance than GaAs PHEMTs, are being developed to replace the latter. State of the art noise figures for InP HEMTs are, for example, 0.8 dB at 60 GHz and 1.2 dB at 94 GHz. GaAs based power HEMTs show higher efficiencies than competing MESFETs for frequencies over 10 GHz, and are comparable to them below 10 GHz. In the higher frequency range, the state of the art in the output power of HEMTs gives a −6 dB/octave line connecting 4W at 20 GHz and 0.1 W at 100 GHz. As there are still reliability problems yet to be solved with the low noise InP HEMTs and the power HEMTs, further study of degradation mechanisms in AlInAs/InGaAs/InP systems, r.f. operation testing of really high power HEMTs, systematic reliable data, etc. would be necessary for them to be accepted as having been established to be reliable devices.

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.

Ultra-high throughput of GaAs and (AlGa)As layers grown by MBE with a specially designed MBE system

Ultra-high throughput MBE growth of very pure and extremely uniform GaAs and (AlGa)As layers with excellent surface morphology can be realized using a newly developed MBE system. High throughput can be achieved by the combination of the simultaneous growth of seven 2 inch or three 3 inch epiwafers and of the automatic growth operated continuously day and night, without accelerating growth rates. The surface defect density has been reduced to the allowable level even for GaAs microwave monolithic ICs. Hall mobilities 1 × 105 cm2/V · s at 77 K were routinely obtained from slightly Si-doped GaAs layers. The microwave devices fabricated from the epiwafers grown by this system showed excellent performance.

15 mW Single Mode CW Operation of Crank Structure TJS Laser Diodes at High Temperature

A new high power AlGaAs laser with a window structure, crank type TJS laser, has been developed. The laser operates in a fundamental transverse mode even at 20 mW CW power. The threshold current is reduced to as low as 20 mA by shortening the crank length of the laser and the diode oscillates even above 80°C. The maximum power of the diode is nearly ten times higher than that of a conventional TJS laser. Maximum powers of 200 and 40 mW are obtained in pulsed and CW operation, respectively. Static characteristics of the diodes and interim status of long term operation are described.

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.

Selective-area MOCVD growth for 1.3 μm laser diodes with a monolithically integrated waveguide lens

A tapered thickness profile and a high thickness enhancement ratio of 3.5 in the waveguide which are necessary for a narrow beam have been realized by selective-area metalorganic chemical vapor deposition (MOCVD) growth using a tapered shape twin mask. A multiple quantum well (MQW) active layer with high strain of 0.9% which is effective for a low threshold current has also been successfully grown by the control of the compositional modulation of InGaAsP in the selective-area growth. Using these techniques, a narrow beam and a low threshold current have been realized for a 1.3 μm laser diode monolithically integrated with a tapered thickness waveguide lens.

Less than 10 defects/cm2 · μm in molecular beam epitaxy grown GaAs by arsenic cracking

Abstract Drastic reduction of irregular defect density in molecular beam epitaxy (MBE) grown GaAs is obtained by using a novel arsenic Knudsen effusion cell with a cracking furnace. A surface defect density of less than 10 cm −2 is routinely achieved for continuously grown three 3-inch diameter, 1.7 μm thick, metal-semiconductor-field effect transistor (MESFET) structures when the cracking is carried out at about 700°C, which is the critical temperature for the conduction type change, and with the group III Knudsen cell only heated near the orifice of the crucible (top heat cell). These optimized cracking conditions also lead to successful mass production of some microwave devices with not only ultra-low defect density but suitable electrical performances.

Manufacturability and reliability of InP HEMTs

Abstract This article describes the present status concerning manufacturability and reliability of InP HEMTs ( n -AlInAs/InGaAs/InP HEMTs) towards the practical use. The precise and reproducible control in the gate recess etching for the InP HEMTs was realized by employing the highly selective pH-adjusted citric acid based solution. The 0.15 μm-length T shaped gate InP HEMT fabricated on 3 inch wafers by the selective recess etching showed a minimum noise figure as low as 0.9 dB with an associated gain of 7.0 dB at 60 GHz and a standard deviation in I dss as low as 3.2 mA. These successful results promise the good manufacturability of the excellent performance InP HEMTs with high yield. The present reliability of the InP HEMTs is at least one order lower than that of conventional GaAs based HEMTs because of their poor thermal stability. It is demonstrated that the main reason for the thermal instability of the InP HEMTs originates from the donor passivation in the n -AlInAs electron supplying layer caused by fluorine during the thermal stress and that this donor passivation is peculiar to the materials containing both AlAs and InAs. The mechanism of this peculiar donor passivation and some ideas for the suppression of it is discussed.

Improvement of crystal quality and laser characteristics by zero net strain structure

Zero net strain structure is very useful for strained multiple quantum well (MQW) lasers for which many numbers of quantum wells are required. We demonstrate the effectiveness of the zero net strain structure to prevent the degradation of the crystal quality up to 15 wells, which cannot be realized by the conventionally strained MQW (well: 1.5% compressive strain, 30 A thick). We also show that the zero net strain structure has finite critical thickness and dislocations other than 60° misfit dislocations are introduced into the zero net strain structure beyond the critical thickness. Narrower distribution of threshold current than that of the conventionally strained lasers, high relaxation oscillation frequency of 5.5 GHz/√mW and high differential gain of 6.3 × 10 −16 cm 2 have been realized for the 1.55 μm laser with zero net strain MQW with 15 wells by the suppression of degradation of crystal quality