2 180 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-27, NO. 1 1 , NOVEMBER 1980

field patterns exhibit single mode behavior. The pulse response of the translaser was measured with a rise time of 1 nsec. CW operation of the device with the substrate bonded to a copper heat sink was obtained.

MP-B2 Single Longitudinal Mode MOCVD GaAlAs-GaAs Self- Aligned Structure Lasers'-J. J. Coleman and P. D. Dapkus, Rockwell International, Electronics Research Center, Anaheim, CA 92803.

We report self-aligned structure GaAlAs-GaAs double-hetero- structure lasers prepared by metalorganic chemical-vapor depo- sition (MOCVD) which operate at low threshold currents on a single longitudinal mode. It was reported recently' that single- mode laser operation could be obtained from InGaAsP-InP double heterostructures having a self-aligned (SA) structure. We have fabricated similar structures in MOCVD GaAlAs-GaAs using a two-step (interrupted) growth process. The four-layer first growth step proceeds as follows: 1) n-GaAlAs, 2 pm, 2) undoped GaAs, 700-1000 8, 3) p-GaAlAs, 0.2-0.5 pm, and 4) n-GaAs (or Gal -xA1xAs, x < 0.10), 0.4-0.4 pm. With conventional photolithographic techniques, 4-8-pm wide stripes are etched through the n-type GaAs layer and into, but not through, the p-GaAlAs layer. This structure is then over- grown with: 1) p-GaAlAs, 1.8 pm, and 2) p+-GaAs, 0.15 pm. In the etched stripe region, the second p-GaAlAs layer com- pletes the optical cavity while the unetched n-GaAs provides current confinement and in that region spoils the optical cav- ity. In this manner we have fabricated SA GaAlAs-GaAs laser devices with single longitudinal-mode laser emission at room temperature and average pulsed threshold currents (length 300-500 pm) less than 65 mA. CW threshold for the same de- vices is about 20 percent higher for diodes bonded directly to TO5 headers. In addition, the quality of these devices indicates that there is no problem associated with the GaAlAs-GaAlAs interface that results from the interrupted MOCVD growth process. The preparation and properties of these devices, in- cluding threshold and emission behavior, will be described in detail.

'This work supported in part by Naval Research Laboratories Con-

'H. Nishi et al., Appl. Phys. Lett., vol. 35, p. 232,1979. tract 173-79-C-0025.

MP-B3 Sinusoidal Modulation Characteristics of Zn-Diffused (GaA1)As Double-Heterostructure Window Lasers of Varying Diffusion Depths-E. Bourkoff, D. Kerps, and R. W. H. Engel- mann, Solid State Laboratory, Hewlett-Packard Laboratories, Palo Alto, CA 94304.

The direct sinusoidal modulation characteristics of Zn- diffused (GaA1)As double-heterostructure window' and non- window' lasers for varying diffusion depths is investigated in addition to the dynamic effects of the window regions. It is well known that the deep Zn diffusion enhances the lateral confinement of both the carriers and optical fields, whereas

'H. 0. Yonezu, M. Ueno, T. Kamejima, and I. Hayashi, IEEE J. Quantum Electron., vol. QE-15, p. 775, 1979.

*K. Kobayashi, R. Lang, H. Yonezu, Y. Matsumoto, T. Shinohara, I. Sakuma, T. Suzuki, and 1. Hayashi, IEEE J. Quantum Electron., vol. QE-13, p. 659, 1977.

the window region substantially increases the threshold of catastrophic optical damage on the cleaved facets, thereby permitting operation with higher optical power. However, the dynamic effects of these structure modifications have not yet been reported. By means of computer-controlled experi- m e n t ~ , ~ the small-signal sinusoidal modulation characteristics were studied. When the Zn-diffusion front is confined to the region above the active layer (conventional planar stripe laser), resonance behavior is typical and independent of diffusion depth. It is possible to bias these layers to obtain a 3-dB band- width greater than 2.6 GHz (the frequency limit of our present automated system). For Zn-diffused stripe lasers with the diffusion front below the active region, the dynamic behavior versus diffusion depth depends on the presence or absence of a window region. The frequency response of the window-stripe lasers (50-pm window regions near each facet) was independent of diffusion depth, exhibited no resonances, and had excellent dynamic linearity. For the case of the continuous-stripe lasers, the dynamic behavior was very dependent on the diffusion depth, with resonant behavior occurring for shallow diffusion and suppression of resonances for deeper diffusion ("1 pm deep).

3We would like to thank Bill Brown and Pete Szente for their assis- tance in the initial stages of the experiment.

MP-B4 Diode Lasers With Lens-Like Active and Cladding Regions-D. R. Scifres, R. D. Burnham, W. Streifer, and D. Fekete, Xerox Palo Alto Research Center, Palo Alto, CA 94304.

We report the operation of diode lasers with lens-like active and cladding regions. The devices are fabricated by a single LPE growth on an n-GaAs substrate into which a 5-pm-wide channel has been etched. By controlling the growth time and cooling rates, layers which are thicker in the center and taper down toward the edges are grown. Both double-heterostructure lasers, in which the active layer is approximately two times thicker above channel center than at the edge, and asymmetric large optical cavity devices in which both the cladding and active layers vary in thickness above the channel have been tested. Such a lens-like geometry creates a lateral waveguide structure which provides kink-free laser operation.

Lasers of the double-heterostructure type have been shown to exhibit thresholds in the range of 23 to 30 mA for 150-pm- long lasers, with linear light output power versus current char- acteristics to -15 mW per facet and differential quantum efficiencies of 40 to 10 percent.

Asymmetric large optical cavity lasers of similar length ex- hibit thresholds of from 35 to 40 mA, have linear P versus I characteristics up to 35 mW pulsed and have been operated in the lowest order transverse mode to 25 mW CW. Again the differential quantum efficiencies exceed 40 percent. Because of the strong real refractive index lateral waveguiding, the half- power width of the mode in the near field is measured to be -1.5 pm which agrees very well with analytic results.

Lasers with lens-like active and cladding layers tend to ex- hibit lower thresholds and higher differential quantum effi- ciencies than CSP lasers' since they do not rely on radiative coupling loss to provide lateral waveguiding. In addition, owing to the variation in active layer thickness, the injected charges diffuse toward the thickest part of the active region where they couple most efficiently to the optical field. However, be- cause of the strong lateral waveguiding, care must be taken in the laser design to avoid oscillation in high order transverse

K. Aiki, et al., IEEE J. Quantum Electron., vol. QE-14, p. 89,1978.