Improved slope efficiency in a VCSEL can be accomplished by selecting particular mirror layer compositions and/or mirror layer configurations that minimize increased reflectivity in the top mirror and/or maximize increased reflectivity of the bottom mirror with increasing temperature. Improved reflectivity of the bottom mirror compared to the top mirror over a desired operating temperature range can be facilitated by (i) selecting mirror pairs for the bottom and/or top mirror that gives the bottom mirror pairs a greater increase in contrast ratio with increasing temperature compared to the top-mirror pairs, and/or (ii) including fewer mirror pairs in the bottom mirror than the number of mirror pairs that would give optimal reflectivity.