Quantum well diode lasers of lead-europium-selenide-telluride

Abstract

The formation of a new semiconductor compound, lead-europium-selenide-telluride, was recently demonstrated using the molecular beam epitaxy (MBE) growth technique. This material may be grown lattice matched to PbTe substrates, and double heterojunction diode lasers were fabricated which covered the wavelength range 6.6 to 2.7 μm. Operation up to 147 K has been attained, which is the highest cw operating temperature ever observed in lead-chalcogenide semiconductors. Single quantum well diode lasers in a lead-chalcogenide materials system have now been fabricated for the first time. These devices were composed of PbTe quantum wells with Pb1−xEuxSeyTe1−y confinement layers. The quantum wells ranged in thickness from 300 to 2500 Å. Strong quantum effects are observed for the smaller well widths (Lz ≲1200 Å) because of the small carrier masses (me∼mh∼0.037m0). The shift in laser emission energy is in approximate agreement with that calculated from a finite square well potential if ΔEc∼ΔEv is assumed. The near equality of the electron and hole effective masses makes it difficult to accurately determine ΔEc and ΔEv. The threshold current is strongly reduced by quantum effects, apparently because of modifications of the density-of-states function. The laser emission from these devices has been characterized by near-field and far-field measurements. At high temperatures (T≳90 K), the emission of these mesa stripe lasers switches from gain guided to an index guided mode. Single-mode emission up to ∼1-mW power levels have been observed. These lasers have tuned from 6.45 μm (at 13 K) to 4.41 μm (at 174 K) under cw conditions, and to 4.01 μm (at 241 K) pulsed. It appears that the maximum operating temperature is limited by the quantum well barrier height, and a preliminary experiment with a higher barrier gave pulsed operation up to 260 K. These are the highest pulsed and cw operating temperatures ever reported for lead-chalcogenide diode lasers, and puts them within the operating range of thermoelectric coolers. The total cw tuning range of a single diode laser is as large as 740 cm−1, which is also much larger than previously observed. These properties greatly enhance the utility of these devices for spectroscopic and fiber-optic applications.