Influence of structural/material perturbations on the operation of thin p-clad diode lasers

Semiconductor diode lasers of two types with two or more segments and a thin p-clad structure were modeled, fabricated and characterized. The majority of the devices fabricated had an active/passive/active (APA) design such that perturbations to the passive section changed the lasing characteristics in a substantial way.;The first laser type studied operated near 950 nm. The 950 APA-type lasers were fabricated from thin p-clad material in which the mode loss in the passive section is determined primarily by free carrier absorption in the cap layer. Calculations show that changing the cap thickness (tcap) from 100 nm to 220 nm changes the loss of the fundamental transverse mode by a factor of about 20. For tcap values greater than 150 nm, a first order guided mode is allowed, and for tcap values greater than 220 nm, this mode is the lowest loss mode in the passive section. Its loss decreases by about a factor of 20 as tcap increases from 220 nm to 340 nm.;The second laser type studied operated near 760 nm. The 760 APA lasers were fabricated from thin p-clad material in which the mode loss was determined primarily by interband absorption in the upper-guide layer. For both laser types, the mode loss in the passive section is also dependent on the loss and refractive index of materials placed on the surface of the passive section.;Standard lasers with different cavity lengths were fabricated from the 950 and 760 materials. Characterization results were then used to determine certain fundamental lasing parameters of the materials. Various types of 950 APA devices were fabricated including those with different tcap values in the passive section and Ni or Au coatings in a portion of the passive section. Characterization results were in good agreement with modeled results. APA devices with an absorbing dye film on the surface of the passive section were also fabricated. Characterization tests showed that the dye increased threshold current and lowered slope efficiency as expected. It was found that these changes could be reversed when the dye film was removed. The APA devices fabricated from the 760 material showed a "snap-on," "snap-off" behavior characteristic of devices containing a saturable absorber, as well as a spatial mode beating phenomenon in the passive section. Reasons for this behavior and practical application of both APA device types as chemical sensors are addressed.