Abstract: A semiconductor laser having a high modulation bandwidth is made by utilizing an InGaAsP cap layer and an InGaAsP active layer of different crystal structure. Channels are anisotropically etched through the cap, cladding and active layers and partially through the buffer layer. The active and cap layers a laterally etched and a semi-insullating material is overlayed the sidewalls. A further etching leaves a thin wall of the semi-insulating material surrounding the active layer. 1.3 .mu.m InGaAsP lasers with 3 dB bandwidths of 24 GHz and intrinsic resonance frequencies in excess of 22 GHz have been successfully fabricated. This is the highest bandwidth ever reported for a semiconductor laser, and the highest resonance frequency for InGaAsP lasers. Excellent modulation efficiencies are observed to high frequencies.

Abstract: A semiconductor mesa structure is covered with a photoresist material in a localized flooding manner such that the photoresist material is thinner on the top of the mesas and also at the upper most portion of the sidewalls than at the base of the mesa and the intervening channel. The photoresist is then exposed through a mask in a manner so that when developed, the photoresist from the mesa top and upper most portion of the sidewall can be removed. When the photoresist is exposed to the actinic radiaction, the thinner photoresist is adequately exposed more rapidly than the thicker portion nearer the bottom of the mesa, if the mask does not adequately shield the actinic radiation from reaching it. Thus the alignment tolerance is greater than if the photoresist were of uniform thickness.

Abstract: A semiconductor laser having a high modulation bandwidth is made by utilizing an InGaAsP cap layer and an InGaAsP active layer of different crystal structure. Channels are anisotropically etched through the cap, cladding and active layers and partially through the buffer layer. The active and cap layers a laterally etched and a semi-insulating material is overlaid the sidewalls. A further etching leaves a thin wall of the semi-insulating material surrounding the active layer. 1.3 .mu.m InGaAsP lasers with 3 dB bandwidths of 24 GHz and intrinsic resonance frequencies in excess of 22 GHz have been successfully fabricated. This is the highest bandwidth ever reported for a semiconductor laser, and the highest resonance frequency for InGaAsP lasers. Excellent modulation efficiencies are observed to high frequencies.