The ongoing quest for semiconductor lasers with low threshold has led to the development of new materials
(quantum wells, wires, and dots) and new optical resonators (microdisks and photonic bandgap crystals).
In a novel approach to "thresholdless" lasers, we have developed a new growth technique for self-assembled
deep-centers in the technologically important semiconductor gallium-arsenide (GaAs). We recently demonstrated
the first GaAs deep-center laser. These lasers, which intentionally utilize GaAs deep-center transitions, exhibit a
threshold current density of less than 70mA/cm2 in continuous-wave mode at room temperature at the important
1.54 μm fiber-optic wavelength in a single-pass geometry. We studied fast carrier dynamics in the new GaAs
deep-center laser. The low threshold current was a consequence of fast subpicosecond capture of free holes onto
deep-centers. This fast capture of free holes onto deep-centers allowed fast depopulation of electrons out of the
lower energy level of the optical transition. We demonstrated laser action at many wavelengths between 1.2 μm
and 1.6 μm, including fiber-optic wavelengths. A significance is that it has been a long-sought goal to tune
the stimulated-emission from the same semiconductor over a wide wavelength range. A semiconductor source of
tunable coherent radiation would have many applications, e.g., fiber-optics, spectroscopy, lab-on-a-chip, chemical
species identification.
We demonstrate the first LEDs at 1.3-1.5um using GaAs deep-centers having higher (90%)
efficiencies and larger Einstein B-coefficients than bulk InGaAs. An observed absence of deep-center self-absorption
(from a Franck-Condon shift) could make possible near-zero threshold lasers. The fast capture (15-
40fs) of free holes by deep-centers, as well as the Einstein B-coefficient, are deduced from a combination of
photoluminescence and electroluminescence measurements.
Conference Committee Involvement (1)
Ultrafast Phenomena in Semiconductors and Nanostructure Materials XII
20 January 2008 | San Jose, California, United States
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