Preparation and Applications of Lead Chalcogenide Diode Lasers
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PREPARATION AND APPLICATIONS OF LEAD CHALCOGENIDE DIODE LASERS DALE L. PARTIN Physics Department,
General Motors Research Laboratories, Warren, MI
48090-9055 ABSTRACT Lead chalcogenide diode lasers are useful for spectroscopic and fiber optics applications in the mid-infrared (2.5-30 #m) wavelength range. These devices have previously required cryogenic cooling ((100 K) for CW operation. This limitation has been overcome through the use of a new, as well as the introduction lattice-matched alloy system, Pb xEu xSe yTe of advanced, quantum well active region device structures grown by molecular Operating temperatures have been increased to 175 K CW Thermal leakage currents out (at 4.4 usm)and to 270 K pulsed (at 3.9 #m). of the device active region appear to be limiting device performance. This beam epitaxy (MBE).
has led to the study of band offsets in PbEuSeTe/PbTe heterojunctions as well as to exploration of alternative high energy band gap alloys of PbTe The status of this work and examples of ultrawith Ge, Yb, Ca, Sr, and Ba. high resolution studies done with these tunable laser sources will be included.
INTRODUCTION Lead-salt diodes provide tunable laser sources in the 2.5 to 30 pm This wavelength range can be covered with either wavelength range [1-5]. the PbCdS, PbSSe, and PbSnSe material systems or with PbGeTe and PbSnTe. The devices often have multimode emission and limited CWoperating temperatures (0.5
Pb 1.)CaxTe
C/
Pbl.xSr)Te
Wu
0.4-
0.3
I
0 Fig. 7
I
0.1 0.2 Composition (X)
0.3
Energy band gap at 300 K vs. composition for PbTe-based ternary compounds.
We have recently studied the properties of MBE grown PbCaTe, PbSrTe, and PbBaTe [36,37].
Several materials properties were explored, including the dependence of energy band gap on alloy composition (see Fig. 7). The curve for PbBaTe is not included since BaTe appears to have a small solubility in PbTe. From the figure, it is seen that increases in energy band gap are roughly comparable for PbEuTe, PbCaTe, and PbSrTe. Thus, their relative merits for diode lasers may be determined by factors such as energy band offsets, which have not yet been determined for PbCaTe/PbTe and PbSrTe/PbTe heterojunctions. In other recent work, PbCdSSe/PbS latticematched double heterojunction diode lasers have been grown by MBE with pulsed operation up to 200 K at an emission wavelength of 3.27 #m [38]. Despite the problem with Cd diffusion into PbTe mentioned earlier, there may be a possibility of using CdTe/PbTe heterojunctions for diode laser applications. As shown in Fig. 6, such heterojunctions would be nearly lattice matched at room temperature (Aa/a = 0.3%), and give a large change in energy band gap. epitaxy [39,40], epitaxy [43].
Such heterojunctions have been grown by hot wall
ionized cluster beam epitaxy [41,42],
and molecular beam
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TUNABLE DIODE LASER APPLICATIONS The fundamental characteristics of lead salt diode lasers which make them useful for various applications are listed below. Coverage of the wavelength range 2.5-30 #sm. Ease of tun
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