Defect Studies of GaP Crystals Pulled from Nonstoichiometric Melts: Dislocation and ``Saucer'' Etch Pits

Abstract

It has recently been shown that the occurrence of flat‐bottomed saucer‐shaped etch pits (S‐pits) in GaP grown by the liquid‐encapsulated‐Czochralski (LEC) technique can be correlated with reduced photoluminescence (PL) and electroluminescence (EL) efficiencies. At the same time a new class of LEC crystals pulled from nonstoichiometric melts (LEC/NSM) have become available which show much improved PL efficiencies (η). A study of the etchpit densities in LEC/NSM crystals was therefore carried out. Both p‐ and n‐type material were examined. In n‐type material the S‐pit density is reduced by at least 4 orders of magnitude for all LEC/NSM crystals compared with LEC material. Similar reductions in S‐pit density are observed in p‐type material, but only for crystals pulled from melts containing less than 30 at. % phosphorus. This correlates well with those p‐type crystals showing major improvements in PL η. However, crystals pulled from 20 and 10 a/o P melts are small in size and have a strong tendency to entrain pockets of gallium. The most promising LEC/NSM samples are the low or zero S‐pit density n‐type crystals pulled from 36 and 30 a/o P melts. Since these crystals have no Ga inclusions, are very low in dislocation density, and can be grown to reasonably large diameters (greater than 15 mm), they are expected to be quite useful as substrates for diffused or single‐tipped LPE p/n junction EL devices. In fact, preliminary measurements have shown that the EL η of red‐emitting diodes fabricated on LEC/NSM substrates equals the best reported values (∼2%) at 10 mA for single‐tipped 0.015‐in.‐square LPE devices.