H. Asahi

New semiconductors TlInGaP and their gas source MBE growth

New III-V compound semiconductors Tl x In 1-x-y Ga y P (thallium indium gallium phosphide), which we proposed recently for 0.9 μm to over 10 μm laser diodes, are grown by gas source molecular beam epitaxy on InP and GaAs substrates for the first time. They have a potential to exhibit a temperature-independent band-gap energy. Grown layers exhibit (2 x 4) surface reconstruction. X-ray diffraction measurements show the successful growth of TlInP, TlGaP and TlInGaP, although phase separation is observed in TlGaP grown on GaAs. Photoluminescence emission is observed for TlInP and TlInGaP grown on InP. Hall measurements show n-type conduction with a room temperature electron concentration of 6.3 x 10 15 cm -3 and an electron mobility of 2500 cm 2 /V. s.

Photoconductance measurement on TlInGaP grown by gas source MBE

Abstract TlInP, TlGaP and TlInGaP layers are grown by gas source MBE and the temperature-dependence of their band gap energy is characterized with the photoconductance measurement. This material system was recently proposed by us for 0.9xa0μm to over 10xa0μm optical devices as well as temperature-insensitive-wavelength laser diodes. Photoconductance measurements on TlInP and TlInGaP grown on InP substrates show that their band gap energies are narrower than that of InP and that the temperature variation of band gap energy is weaker than those of InP and InAs as expected. Furthermore, photoconductance measurements on TlGaP grown on GaAs substrates show the absorption in the 1.4xa0μm wavelength region as well as the small temperature variation of absorption edge (band gap energy) as expected.

Gas source MBE growth and characterization of TlInGaP and TlInGaAs layers for long wavelength applications

Abstract New III–V semiconductors TlInGaP and TlInGaAs (Tl composition of less than 0.1) are grown on InP substrates by gas source molecular beam epitaxy. They are proposed for long wavelength optical devices as well as temperature-insensitive wavelength laser diodes. Grown layers are characterized by the measurements on the temperature variation of photoconductance and photoluminescence. It is observed that the bandgap energy shows small-temperature variation suggesting the existence of temperature-independent bandgap energy in these material systems for the layers with increased Tl composition.

Observation of Small Temperature Variation of Longitudinal-Mode Peak Wavelength in TlInGaAs/InP Laser Diodes

To fabricate temperature-insensitive wavelength laser diodes (LDs), which are important in the wavelength division multiplexing optical fiber communication system, we have studied TlInGaAs/InP heterostructures. TlInGaAs/InP metal-stripe LDs were fabricated with gas source molecular-beam epitaxy. Current-injection pulsed-laser operation was obtained up to 310 K. Threshold current density and lasing wavelength at room temperature were 7 kA/cm2 and 1660 nm, respectively. The observed temperature variation of the longitudinal-mode peak wavelength was as small as 0.06 nm/K. This value is much smaller than that observed for distributed feed-back LDs (0.1 nm/K). This is considered to result from the addition of Tl into the LD active layer.

Growth of TlInGaAs on InP by Gas-Source Molecular Beam Epitaxy

TlInGaAs quaternary layers are grown on InP substrates by gas-source molecular beam epitaxy (MBE) for the first time. The application of TlInGaAs was proposed for long-wavelength optical devices as well as temperature-insensitive wavelength laser diodes. During the growth, RHEED (reflection high-energy electron diffraction) patterns show (2×2) reconstructions. Successful growth of TlInGaAs is confirmed with X-ray diffraction measurements. PL emission is observed and the temperature variation of PL peak energy is as small as 0.1 meV/K.

Reduced temperature dependence of refractive-index in TlInGaAs quaternary alloys grown on InP substrates

Refractive-index dispersion for the TlInGaAs quaternary alloys, grown on (100) InP substrates by gas-source molecular-beam epitaxy, has been measured at temperatures from 290 to 350 K in the photon-energy range of 1.2–2.0 eV by using spectroscopic ellipsometry. The temperature coefficient of the refractive-index decreases with increasing Tl composition. The result corresponds to the already reported reduced temperature dependence of the band-gap energy for the TlInGaAs because of the alloy of semiconductor InGaAs and semimetal TlAs. The result also agrees with the recently reported small temperature-variation of the lasing-wavelength for the TlInGaAs/InP laser diodes.

Temperature-Stable Wavelength TlInGaAs/InP Double Heterostructure Light-Emitting Diodes Grown by Gas Source Molecular Beam Epitaxy

TlInGaAs/InP double heterostructure light-emitting diodes were grown on (100) InP substrates by gas source molecular beam epitaxy. The Tl composition was 6%. They were operated at up to 340°C with a wavelength around 1.58 µm. Very small temperature dependence of the electroluminescence peak energy (-0.09 meV/K) was observed, which is similar to the temperature dependence of the photoluminescence peak energy.

Gas source MBE growth of TlInGaAs/InP laser diodes and their room temperature operation

Abstract Tl-containing III–V semiconductors are expected to produce temperature-insensitive wavelength laser diodes, which are important in wavelength division multiplexing optical fiber communication systems. TlInGaAs/InP double heterostructure lasers were grown by gas source MBE. Temperature variation of electroluminescence emission peak wavelength as small as 0.064xa0nm/K (0.047xa0meV/K) was observed. Current injection pulsed laser operation was obtained up to 310xa0K. The threshold current density was about 5xa0kA/cm 2 at 1.66xa0μm at room temperature. T 0 value was about 90xa0K. CW operation was also obtained at 77xa0K.

First successful growth of TlInGaAs layers on GaAs substrates by gas source MBE

Abstract To realize the temperature-stable threshold-current and lasing-wavelength 1.3–1.5xa0μm laser diodes, TlInGaAsN/AlGaAs heterostructures were proposed. As a first step, TlInGaAs was successfully grown, for the first time, on GaAs substrate by molecular beam epitaxy. The incorporation of Tl was confirmed with reflection high-energy electron diffraction intensity oscillation measurement. Photoluminescence (PL) measurements were conducted on the TlInGaAs/GaAs and InGaAs/GaAs heterostructure samples and the red shift of the PL peak energy was observed for the TlInGaAs/GaAs samples, as expected.

Gas source MBE growth of TlInGaAs/InP DH structures for the application to WDM optical fiber communication systems

Abstract TlInGaAs/InP double heterostructures (DHs) were grown on (1xa00xa00) InP substrates by gas source MBE. The photoluminescence (PL) peak energy and its variation with temperature decreased with increasing Tl composition. For the DH with a Tl composition of 13%, the PL peak energy varied only slightly with temperature (−0.03xa0meV/K). This value corresponds to a wavelength variation of 0.04xa0nm/K and is much smaller than that of the lasing wavelength of InGaAsP/InP distributed feedback laser diodes (0.1xa0nm/K). The TlInGaAs/InP light emitting diodes were also fabricated and the similar small temperature variation for the electroluminescence peak energy was observed. The results are a great first step to realize the laser diodes with temperature insensitive lasing wavelength characteristics, which are important in the wavelength division multiplexing (WDM) optical fiber communication systems.