Double Heterojunction Diode Lasers Research Articles

Heterojunction Stripe Geometry Lead Salt Diode Lasers Grown By Molecular Beam Epitaxy

Abstract. Lead-rare earth-chalcogenide diode lasers have been grown by molecular beam epitaxy. Emission wavelengths shorter than 5 to 6 Am have been obtained from lead-europium-selenide-telluride (Pb1 -xEuxSeyTe1-y) double heterojunction diode lasers grown lattice-matched to PbTe substrates. Mesa diodes with -25 um wide stripes have been fabricated that have a wide range of single longitudinal mode emission at up to -1 mW/facet output power. These diodes have operated at up to 147 K cw, which to our knowledge is the highest cw operating temperature ever achieved with lead-chalcogenide diode lasers. The wavelength coverage of the PbTe system has so far been extended to 4.06 um cw. Longer wavelength coverage is obtained from double heterojunction diode lasers with Ma1-ySnyTe active regions lattice-matched to (Pb1-ySny)1-xYbxTe confinement layers. I n preliminary studies of diodes with x = 0.034, y = 0.14, the cw emission wavelength varied from 10.7 µm (at 10 K) to 7.1 µm (at 128 K).

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

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.

Diode lasers of lead-europium-selenide-telluride grown by molecular beam epitaxy

It is desirable to extend the wavelength coverage of PbSnTe diode lasers to shorter wavelengths (λ<5 μm) and higher operating temperatures. Currently, this range is covered by PbSxSe1−x diode lasers operating below 100 K. Double heterojunction diode lasers have now been fabricated using a new materials system, Pb1−xEuxSeyTe1−y. These structures were grown lattice matched to (100) oriented PbTe substrates by molecular beam epitaxy using PbTe, Eu, Te, PbSe, Tl2Te (p dopant), and Bi2Te3 (n dopant) source ovens. Mesa diodes were fabricated with 20-μm-wide stripes using anodic oxide insulation. Diodes have so far been fabricated with up to x=0.010, y=0.011, which operated cw from 4.93 μm (at 30 K) to 4.06 μm (at 136 K). Diodes with x=0.0015, y=0.0020 have operated up to 147 K cw. This is the highest cw operating temperature ever attained with lead-chalcogenide diode lasers. A wide range of single mode operation with ∼1 mW output power was observed for some of the better diodes. These diodes are useful for ultrahigh resolution spectroscopy, and may be useful in the future for low-loss, long-wavelength fiber optics communications.

The effect of facet mirror reflectivity on the spectrum of single-mode CW constricted double-heterojunction diode lasers

In this paper we show that the spectral mode content of mode-stabilized constricted douhle-heterojunction lasers can be altered by changes in facet reflectivity. If the facet reflectivity is substantially reduced below the nominal value of 30 percent, then the lasers will exhibit multilongitudinal mode operation. Nearly planar-geometry lasers that show instabilities can be made to operate in a stable single mode by increasing the facet reflectivity to values above 50 percent.

Low-threshold high- T o constricted double heterojunction AlGaAs diode lasers

Constricted double heterojunction diode lasers of relatively low CW thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. These values are obtained while still using standard 10 microns wide oxide-defined stripe contacts. Over the 20-70 C temperature interval, threshold current temperature coefficients as high as 320 C and a virtually constant external differential quantum efficiency, are found.

Analysis of grating-coupled emission in lead-tin telluride diode lasers

The use of the grating-coupled emission concept with lead-tin telluride double-heterojunction diode lasers is analyzed theoretically. The GCE configuration is shown to be attractive for producing small divergence-angle emission from fixed-wavelength lead-salt devices, but to be of more limited interest for use with tunable lasers because of the small critical angle characteristic of the PbTe-air interface and because of the variation of the angle of emission with wavelength. The device structure studied is one incorporating a reflecting contact in close proximity to the grating, a feature which leads to resonant enhancement or reduction of the emission, depending upon the wavelength and the device dimensions.

The GaAs P-N-P-N laser diode

The general structure of double-heterojunction diode lasers is shown to be consistent with the required geometry of the Shockley diode or p-n-p-n switch. When the two devices are combined in a single structure, there results an extremely simple source of high optical power (>0.5-W) pulses of very short duration (<10 ns) without the need for a complex external driver. In principle, pulse triggering and repetition rate are easily controlled, suggesting that the device has potential application in pulse-coded optical communication systems.