Dislocations in vapor phase epitaxial GaP
Dislocations in VPE GaP grown on (100) oriented LEC GaP substrates have been characterized, and their origins and effects on LED performance have been investigated. In non-nitrogen doped epilayers, the dislocations are found to originate in the substrate and propagate through the epilayers in straight lines in  and <211> directions. The dislocation density of the epilayer is found to be nearly equal to that of the substrate. Introduction of nitrogen during growth of the epilayer has been observed to bend these so-called “inclined≓ dislocations propagating through the layer into [0−1 1] directions in the (100) plane and thus produces segments of [0 −1 1] dislocations to relieve the lattice parameter mismatch due to N. The mismatch dislocation density is observed to be proportional to the N doping level. At very high N doping levels, > 1019 cm-3, a large number of new inclined dislocations are observed, which may be in part due to GaN precipitation. The effects of dislocations on LED properties were investigated by measuring dislocation densities in the individual diodes using the electron beam induced current mode of the SEM and comparing this with the spot brightness and luminous flux. The dislocations were observed to produce dark spots in the EL emission in many cases. For a series of runs where all growth and processing parameters were fixed, a good correlation between B/J and dislocation density was observed with B/J decreasing with increasing dislocation density in the range < 1 × 104 cm−2 to 1 × 106 cm−2.
Key wordsdislocations GaP VPE GaP green LEDs
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