Stripe geometry lead-telluride diode lasers grown by molecular beam epitaxy

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Abstract
Lead-telluride homojunction diode lasers suitable for ultrahigh resolution spectroscopy have been fabricated using molecular-beam epitaxial (MBE) growth and a mesa stripe geometry. A low-MBE substrate growth temperature of 260 °C was used to minimize interdiffusion during growth. These lasers operate up to 115 K cw with emission in the 6.5–5.0-μm wavelength range. The threshold current density follows the relation J=J0 exp(T/T0) up to 100 K, with J0=110 A/cm2 and T0=26.0 K. Thermal resistance effects cause a departure from this relationship at higher temperatures. The current-voltage relationship as a function of temperature indicates that tunneling currents contribute significantly to the threshold current density. Single-fundamental mode emission is obtained from 20-μm-wide mesa stripes at high temperature, whereas a higher order mode is observed with 35-μm-wide stripes. Analysis of the near and far field patterns indicates that the lasing mode is index guided at high temperatures, and gain guided at low temperatures. Single-mode output powers of over 1 mW/facet are obtained in 90–100 K with high-external differential quantum efficiencies (5%–6%/facet).