Red-Emitting III-Nitride Self-Assembled Quantum Dot Lasers
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Visible light sources have numerous applications in the fields of solid state lighting, optical data storage, plastic fiber communications, heads-up displays in automobiles, and in quantum cryptography and communications. Most research and development into such sources is being done using III-nitride materials where the emission can be tuned from the deep UV in AlN to the near infrared in InN. However due to material limitations including large strain, piezoelectric polarization, and the unavailability of cheap native substrates, most visible devices are restricted to emission near GaN at 365 nm up to around 530 nm. Self-assembled InGaN/GaN quantum dots (QDs) can be epitaxially grown in the Stranski-Krastanow growth mode and can overcome many of these limitations.
The first red emitting InGaN/GaN quantum dot lasers, emitting at up to 630 nm have been realized in the present study. These lasers show good performance compared with other material systems, including InGaAlP/GaAs and AlGaAs based red lasers. They are characterized by relatively low threshold current densities (1.6 kA/cm2) and high temperature stability (T0~240 K). The maximum measured output power is 30 mW, making them suitable for the applications discussed above. The lasers have also been characterized by a maximum modal gain of 35 cm-1 and differential gain of 9.0×10-17 cm2. Dynamic characterization of the lasers has also been performed from which a maximum small signal modulation bandwidth of 2.4 GHz has been measured.