PERFORMANCE OF A VALVED ARSENIC CRACKER SOURCE FOR MBE GROWTH

We report on the performance of a valved As cracker source and compare the qualities of GaAs, AlGaAs, and strained InGaAs quantum-well (QW) lasers grown with As2 and AS4 species. By varying the valve position, the As flux can be varied rapidly and controllably without thermal adjustment. The furnace is ruggedly designed to provide satisfactory mechanical and thermal performance. For cracking temperatures (T(Cr)) greater-than-or-equal-to 775-degrees-C where AS2 flux predominates, the undoped GaAs is n-type and the value of electron concentration (n) increases with increasing T(cr). The best cracker cell performance is obtained at T(cr) = 825-degrees-C, which gives n almost-equal-to 2 x 10(14) cm-3 and mu77K = 122,000 cm2 V-1 s-1 in undoped GaAs. For T(cr) less-than-or-equal-to 750-degrees-C, the undoped GaAs is p-type and the furnace operates essentially in As4 mode. The photoluminescence spectrum is typical of high quality GaAs grown with AS4. Deep level transient spectroscopy does not detect any electron deep levels in As2-GaAs. Although strained InGaAs QW lasers grown using AS2 at a substrate temperature as low as 570-degrees-C have a lower threshold current density, they also exhibit a 10-25% lower differential quantum efficiency as compared to the AS4 counterpart in which the AlGaAs cladding layers are grown at approximately 700-degrees-C.