Effects of growth temperature and V/III ratio on surface structure and ordering in Ga0.5In0.5P

Surface photoabsorption (SPA) measurements were used to clarify the CuPt ordering mechanism in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The CuPt ordering is known to be strongly affected by the growth temperature and the input partial pressure of the phosphorus precursor, i.e. the V/III ratio. The SPA peak at similar to 400 nm was found to be a measure of the concentration of [<(1)over bar 10>]-oriented phosphorus dimers on the surface, which are characteristic of the (2 x 4) reconstruction. Both ordering, measured using the low temperature photoluminescence peak energy, and the SPA signal difference due to P dimers were studied versus the growth temperature and V/III ratio. The degree of order decreases markedly with increasing growth temperature above 620 degrees C at a constant V/III ratio of 40. This corresponds directly to a decrease of the [<(1)over bar 10>]-oriented P dimer concentration on the surface determined using SPA. Below 620 degrees C, the degree of order decreases as the growth temperature decreases, even though the concentration of P dimers increases. The presence of an isotropic ''excess P'' phase observed in the SPA spectrum at similar to 480 nm might be responsible for the decrease of CuPt ordering, although it has previously been attributed to the slow rearrangement of adatoms. The degree of order is found to decrease monotonically with decreasing V/III ratio in the range from 160 to 8 at 670 degrees C and from 40 to 8 at 620 degrees C. This also corresponds directly to the decrease of the P dimer concentration on the surface measured using SPA. At 620 degrees C and a V/III ratio of 160, the degree of order decreased despite an increase of the P dimer concentration. This may also be due to the formation of the isotropic ''excess P'' phase on the surface. The direct correlation of the [<(1)over bar 10>]-oriented P dimer concentration and the degree of order with changes in temperature (greater than or equal to 620 degrees C) and V/III ratio (less than or equal to 160 at 670 degrees C and less than or equal to 40 at 620 degrees C) suggests that, in this range of growth parameters, the (2 x 4) surface reconstruction is necessary to form the CuPt structure, in agreement with published theoretical studies.