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The growth rate evolution versus V/III ratio and substrate temperature was studied by means of optical reflectivity during MBE of GaN layers using NH 3 as nitrogen source. The GaN desorption becomes observable at temperatures above 800 ° C and causes the reduction of growth rate accompanied with the surface roughening at temperatures above 850-870 ° C. Unlike GaAs, which evaporates in accordance with the action mass law, the desorption rate of GaN is found to be almost independent of V/III ratio within the N-rich growth conditions. The activation energy for GaN desorption during the growth is found to be (3.2 ± 0.1) eV. This value is very close to the activation energy for free evaporation. At V/III ratio values exceeding 200 the GaN growth rate reduction caused by violation of the molecular flow regime is observed. The Mg-doped samples grown under these extreme conditions tend to have improved acceptor activation and thus p-type conductivity.

The nature of optical confinement in phase-locked laser arrays (PLLAs) with a mesa-stripe structure (MSS) has been studied. Two main mechanisms are distinguished, which are based on the variation of the waveguide effective refractive index due to MSS formation and on the refractive index modulation induced by the heating of the structure. Stable operation was achieved when either weak or strong optical coupling was realized in the PLLA. A phase-locked regime of radiation was obtained only for laser diodes with strong optical coupling. In the latter case the angle divergency was not greater than 2 • for the antisymmetric supermode emission from the PLLA.

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The influence of the growth temperature of ternary compounds on the degradation rate of AlGaAdGaAs laser diodes was studied. The optimal temperature was found to be 700 "C. A further reduction in the degradation rate may be achieved by using a ridge-type stripe-array contact instead of a broad-area contact. The percentage of diodes with a lifetime exceeding 2500 hours (at Pout = 2 mWpm-' per facet) was four times larger for the former laser than for the latter.