Short-wavelength laser diodes based on AlInAs/AlGaAs self-assembled quantum dots

Self-assembled quantum dots (QDs) of highly strained InAlAs have been grown by molecular beam epitaxy in separate-confinement p-i-n heterostructures o n (001) GaAs substrates. Results from a systematic study of samples with va rying amounts of deposited material relates the observed emission peaks wit h QD levels, wetting layer states, or barrier materials. For samples with h igh-QD concentration, lasing is observed in the upper-QD shells. A sample w ith contact layers improving carrier and optical confinement operates up to room temperature and displays lowered threshold current densities. A thres hold current density of similar to 4 A/cm(2) is measured for this structure at T = 5 K and continuous-wave operation is obtained up to T similar to 77 K. A material gain larger than 1.7 x 10(4) cm(-1) is measured for this sin gle-layer structure. Lasing is observed in the upper-QD shells for small ga in media, and progresses towards the QD lower states for longer cavity leng ths representing an emission shift of 45 meV. A minor dependence of the thr eshold on QD density is found for samples having densities between 20 and h undreds of QDs per micron squared. For samples with multiple QD layers disp laying vertical self-assembling, an increase in the emission linewidth is o bserved compared with single-layer samples and multilayer samples with unco rrelated growth. (C) 2000 American Institute of Physics. [S0021-8979(00)048 03-9].