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In light of the substantial performance advantages of quantum well lasers relative to double heterostructure lasers, extensive efforts have been directed toward producing quantum wire (QWR) systems. Theory predicts that quantum wire lasers will provide lower threshold current density, increased modulation bandwidth, and improved temperature stability. Despite these predictions, however, progress has been hampered by the extreme difficulty inherent in the realization of multidimensionally confined systems in the laboratory.
This work documents QWR heterostructure lasers prepared via an in situ epitaxial growth technique that results in the spontaneous periodic lateral ordering of GaInP alloy composition perpendicular to the growth direction. The method employs neither pre-growth substrate patterning nor postgrowth processing and performs optimally using on-axis substrates. The resultant strained QWR structures are directly observed by transmission electron microscopy, which reveals typical QWR cross-sectional dimensions of 5 nm x 10 nm. Strain and reduced symmetry lead to polarization of QWR photoluminescence emission spectra of up to 96% at 77 K and 92% at 300 K and extreme sensitivity of the QWR emission intensity to the excitation source polarization. Photoluminescence emission energies are consistent with a first-order strained QWR calculation.
QWR laser diode devices exhibit highly anisotropic emission characteristics. Threshold current densities are several times lower for cavities that are perpendicular to the QWR axis, and the emission polarization is opposite that from cavities oriented parallel to the QWR axis. A threshold current density of 240A/cm$\sp2$ (850 A/cm$\sp2)$ has been obtained under pulsed conditions at 77 K (300 K). These effects are explained in terms of the QWR potential and the strain field present in the active region.
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