'Influence of carrier transport on wavelength chirp of InGaAs/ InGaAsP MQW lasers', Electron. Lett., 1992, 28, (20), pp. 1911- 1913 3 GRABMAIER, A., SCHOFTHALER, M., HANGLEITER, M., KAZMIERSKI, A., BLEZ, M., and OUGAZZADEN, A.: 'Carrier transport limited bandwidth of 1.55 \un quantum-well lasers', Appl. Phys. Lett., 1993, 62, (1), pp. 52-54 4 NAGARAJAN, R., ISHIKAWA, M., FUKUSHIMA, T., GEELS R, S., and BOWERS, J.E.: 'High speed quantum well lasers and carrier transport effects', J. Quantum Electron., 1992, QE-28, (10), pp. 1990-2008 5 ISHIKAWA, M., NAGARAJAN, R., FUKUSHIMA, T., WASSERBAUER, J., a n d BOWERS, J.E.: 'Long Wavelength High Speed Semiconductor Lasers with Carrier Transport Effects', J. Quantum Electron., 1992, QE- 28, (10), pp. 2230-2241 6 YAMAZAKI, H., YAMAGUCHI, M., KITAMURA, M., and MITO, I.: 'Analysis of FM efficiency of InGaAs/InGaAsP SCH-MWQ LDs taking injection carrier transport into account', Photonics Technol. Lett., 1993, 5, (4), pp. 396-398 7 NAGARAJAN, R., and BOWERS, J.E.: 'Effects of carrier transport on injection efficiency and wavelength chirping in quantum well lasers', J. Quantum Electron., 1993, QE-29, (6) 8 HIRAYAMA, H., YOSHIDA, J., MIYAKE, Y., and ASADA, M.: 'Estimation of carrier capture time of quantum well lasers by spontaneous emission spectra', Appl. Phys. Lett., 1992, 61, (20), pp. 2398-2400 9 KAN, s.c, VASSILOVSKI, D., wu, T.c, and LAU, K.Y.: 'On the effects of carrier diffusion and quantum capture in high speed modulation of quantum well lasers', Appl. Phys. Lett., 1992, 61, (7), pp. 752-754 10 KAN, s.c, VASSILOVSKJ, D., wu, T.C, and LAU, K.Y.: 'Quantum capture limited modulation bandwidth of quantum well, wire and dot lasers', Appl. Phys. Lett., 1993, 62,' (19), pp. 2307-2309 11 Commercial microwave modelling program : Libra™ , marketed by the EESOF Inc., Westlake Village, CA GalnP/AIGalnP index waveguide-type visible laser diodes with dry-etched mesa stripes T. Yoshikawa, 'Y. Sugimoto, H. Hotta, K. Tada, H. Kobayashi; H. Yoshii, H. Kawano, S. Kohmoto and K. Asakawa Indexing terms: Semiconductor lasers, Lasers, Reactive ion etching GalnP/AIGalnP index waveguide-type visible-light laser diodes with dry-etched mesa stripes have been fabricated by Cl 2 -reactive ion beam etching for the first time. The AlGalnP cladding layer, which is normally very difficult to dry etch due to problems with Al oxidation and the low volatility of In and its reaction products, was etched smoothly with high depth accuracy. The etched mesa stripes were buried by metal organic vapour-phase epitaxy with- out crystal discontinuity at the regrown surface. The threshold current under room-temperature pulsed operation is 35mA (L = 300 um), which is almost the same value as that for wet-etched lasers. Dry etching has many advantages over wet chemical etching for making the mesa stripes of index waveguide-type visible-light laser diodes (LDs). Uniformity in the full-wafer mass production proc- ess is one such advantage [1]. Control of the etching depth is needed because the thickness of the cladding layer beside the mesa stripe strongly affects the laser characteristics. Anisotropic etching is generally preferred in this case because many visible-light LDs are made from substrates that are misoriented by several degrees to avoid creating natural superlattices and to achieve shorter- wavelength emission [2,3], and wet chemical etching creates asym- metrical mesa shapes on such substrates because of the (11^-ori- ented etching. However, nearly vertical mesa shapes can be obtained by dry etching, even on oriented substrates, because the etching is independent of the surface orientation. A visible-light LD fabricated by dry etching was reported by Unger et al. [4], but the mesa stripe was formed by dry etching only the AlGaAs layer on the thin AlGalnP cladding layer and the etching was stopped at the surface of the AlGalnP cladding layer. No dry-etched visible-light LD with AlGalnP cladding lay- ers has been reported, because AlGalnP is difficult to dry etch due to problems with Al oxidation [5] and the low vapour pressure of In and its reaction products. Previously, we reported the first smooth and vertical etching of AlGalnP materials [6]. In that Let- ter, it was pointed out that the aluminum-containing surface had been protected from oxidation during the etching process by reducing the amount of water in the etching chamber, and that high temperature, low gas pressure and high ion energy etching conditions had promoted the desorption of indium and its reac- tion products. This Letter describes the first attempt to dry-etch a conven- tional visible-light LD. In the experiment, the depth of an etched AlGalnP layer was examined for uniformity. A GalnP/AIGalnP visible-light LD with dry etched mesa stripes was then fabricated, and I-L measurement revealed that its threshold current was com- parable to that of wet etched LDs. A GalnP/AIGalnP double heterostructure was grown by metal organic vapour phase epitaxy (MOVPE) on (001) GaAs substrates with misorientation of 4° toward [110]. The etching mask was a layer of SiO 2 patterned by CF 4 reactive ion etching (RIE) using a photoresist mask. Mesa stripes were fabricated by Cl 2 reactive ion beam etching (RIBE) at the same high temperature (~200°C) and low gas pressure (~10 5 torr) conditions as had been reported pre- viously [5]. The ion acceleration voltage, however, was changed from 1.1 kV to 900 V so as to increase the selectivity to the SiO 2 mask from 2.6 to 3.9. Before regrowth, the surface was etched slightly with an H 2 SO 4 :H 2 O 2 :H 2 O = 3:1:1 etchant to a depth of-60 nm to clean the surface and to remove the etching damage. A cur- rent blocking layer and a cap layer were then grown by MOVPE. 5 10 15 20 distance from centre, mm 15 1960/11 Fig. 1 Etching depth of AlGalnP 2 inch wafer as function of distance from wafer centre The sample was rotated during the etching process so as to increase the etching depth uniformity Height: h, a = 15nm,2.3% Dry etching visible-light LDs gives rise to three particularly desirable features, two of which, controllability and a vertical (ani- sotropic) profile, have been reported before [5]. Thus, our target was the third of these leatures: etching depth uniformity. A single layer of AlGalnP grown on a 2 inch GaAs wafer was etched while being rotated during the etching process. The mesa height h was then measured as a function of the distance from the centre as shown in Fig. 1. As an example of the results obtained, a 0.64 \xm layer was found to have an etch-depth fluctuation of only o = 15 1690 ELECTRONICS LETTERS 16th September 1993 Vol. 29 No. 19