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Metal-cavity submonolayer (SML) quantum-dot (QD) microlasers are demonstrated at room
temperature under continuous-wave electrical injection for 2-μm-radius devices and pulsed
operation for 0.5-μm-radius devices. Compared to our previous quantum well devices, the superior
optical properties of SML QDs provide the possibility for further size reduction. Size-dependent
lasing characteristics are extracted from measurements to investigate the device physics for future
size reduction. An optical cavity model using the transfer matrix and the effective index method
including metal dispersion is developed and used for both the design and the experimental results
analysis. The laser uses an active region consisting of three groups of SML QDs, and each group
consists of 10 stacks of 0.5-monolayer InAs QD layers. The cylindrical microcavity is formed by
hybrid metal-distributed Bragg reflectors (DBRs) mirrors with an optimized SiNx passivation layer
on the sidewall to reduce the metal loss and to avoid the leakage current. The transverse optical
modes are solved using the Maxwell equations, and the resonance condition is determined by roundtrip
phase matching. Vertically-correlated QDs are modeled as quantum disks, and the wave
functions and eigenenergies in both conduction and valance bands are solved from Schrodinger
equation. Carrier-dependent material gain is calculated using Fermi’s golden rule and included in the
model. The lasing wavelengths, quality factors, and confinement factors for cavity modes are the
inputs for the rate-equation model, which predicts the light output power vs. current behavior and
has shown excellent agreement with experiments. Size-dependent physical quantities such as
leakage current and spontaneous emission coupling factor are extracted and investigated. Further
size reduction using only four pairs of DBRs is proposed.
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