GALLIUM ARSENIDE DIODE LASERS WITH OBLIQUE ANGLES BETWEEN RESONATOR MIRRORS AND P-N JUNCTION

Diode lasers have been fabricated in which the junction plane is tilted at angles of ifθ = 0·5-4·5°, in steps of 0·5°, from the normal position at 90° to the cleaved (110) planes forming the Fabry-Perot cavity mirrors. The threshold current as a function of angle has been measured at temperatures of 4·2°, 77° and 195°K. The results are qualitatively similar for all three temperatures; at θ = 1·5° the threshold current j = 2j(0) and at θ = 3·5°, j = 8j(0). A theory, based on the electromagnetic field variation within the active region, is derived to describe the effective reflectivity of the cavity and hence to calculate the variation of threshold current with angle. Good agreement between experiment and theory is obtained for small angles, up to 3·5°. Above this value theory and experiment diverge and the threshold current rises very rapidly. Reasons for this behaviour are discussed. Observation of the far-field pattern indicated only axial modes in a plane perpendicular to the junction plane for all values of θ, in contrast to the predictions of geometrical optics. Finally the results have been used to estimate the accuracy of junction and mirror orientation necessary for InAs and GaAsxP1 - x lasers, leading to values of 7° and 0·5° respectively. © 1968.