COMPARISON OF CHEMICAL BEAM EPITAXY AND METALORGANIC CHEMICAL-VAPOR-DEPOSITION FOR HIGHLY STRAINED MULTIPLE-QUANTUM-WELL INGAASP INP 1.5-MU-M LASERS/

The performance and reliability of strained layer optoelectronic devic es are in general limited by the integrity of metastable heterostructu res. Misfit strain relaxation (and concomitant defects) can be avoided if the structural stability is optimised and elevated temperature exp osure minimized. Chemical beam epitaxy (CBE) holds great promise in st rained layer epitaxy, since by reducing growth temperature the overall thermal budget for epitaxy and processing can be significantly reduce d. The design, epitaxial growth, fabrication and reliability issues re lated to strain and strain-compensated multi-quantum well lasers are f irst considered in order to determine the upper limits of compressive or tensile strain permissible in such structures. The benefits of stra in (both tensile and compressive) on threshold current density are rel ated to the amount of strain in the wells (via the reduction of the Au ger recombination coefficient) and the well width (via the optical con finement factor). It is therefore the strain - well-width product for the active region which is of key interest. In this survey the practic al upper bound to stability is defined theoretically using an energy b alance model, where the effect of strain compensation from oppositely strained barrier layers, balances the strain in the quantum wells and renders the multilayer stack ''strain neutral''. The susceptibility of strained multilayers to defect injection through epitaxial growth and subsequent device fabrication is determined by growth simulation. Usi ng this model as a design tool we have investigated the structural sta bility of a compressively strained multiple quantum well (MQW) laser t hrough the concept of ''effective stress'' for misfit dislocation inje ction. The upper limits for quantum well strain incorporation with and without strain compensation are quantitatively defined in light of re cent laser reliability data. The evolution of the driving force for mi sfit strain relaxation is mapped out through a typical epitaxial growt h sequence highlighting the points in the growth process of highest vu lnerability to defect injection. These design concepts were used to op timize structures for highly strained quantum wells (QWs) in strain co mpensated InGaAs/InP MQW lasers. The stability of strain-compensated M QW laser structures is demonstrated for devices grown by conventional metalorganic chemical vapour deposition.