Abstract
We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of InxGa1−xAs of moderate indium composition (0.3 < x < 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm−1 and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated.
Highlights
InGaAs/GaAs quantum wells (QWs) and In(Ga)As self-organized quantum dots (QDs) are presently utilized as active areas of various high performance optoelectronic devices such as edge-emitting lasers [1], microlasers [2,3,4], solar cells [5,6,7,8,9], etc
In reference [21], the alignment of InAs QDs on very regularly formed multiatomic GaAs steps, produced by step bunching on vicinal (100) substrates, was studied. This approach was used for growing regular arrays of quantum wire (QWR) structures formed along the step edges
More recently Small signal modulation (SSM) response with 3-dB bandwidth up to 20 GHz was demonstrated for the AlGaInAs/InP microdisk laser with active region based on 6 QWs with a radius of 7 μm surrounded by BCB-cladding layer [85]
Summary
InGaAs/GaAs quantum wells (QWs) and In(Ga)As self-organized quantum dots (QDs) are presently utilized as active areas of various high performance optoelectronic devices such as edge-emitting lasers [1], microlasers [2,3,4], solar cells [5,6,7,8,9], etc. The growth and investigation of structural and optical properties of Inx Ga1−x As layers with moderate In concentrations (0.3 < x < 0.5) is expected to be useful for the formation of the aforementioned nanostructures of intermediate 2D-0D dimensionality. In reference [21], the alignment of InAs QDs on very regularly formed multiatomic GaAs steps, produced by step bunching on vicinal (100) substrates, was studied This approach was used for growing regular arrays of quantum wire (QWR) structures formed along the step edges. Another approach to form nanostructures of mixed dimensionality is to apply MOCVD or MBE growth of InGaAs with low In composition [16,25,30].
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