Surface photoabsorption study of the effects of growth temperature and V/III ratio on ordering in GaInP

Abstract

Surface photoabsorption (SPA) measurements were used to clarify the Cu–Pt ordering mechanism in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The Cu–Pt ordering is strongly affected by the growth temperature and the input partial pressure of the phosphorus precursor, i.e., the V/III ratio. SPA was used to measure the concentration of [1̄10]-oriented phosphorus dimers on the surface, which are characteristics of the (2×4) reconstruction, as a function of the growth temperature and V/III ratio. The degree of order decreases markedly with increasing growth temperature above 620 °C at a constant V/III ratio of 40 [tertiarybutylphosphine (TBP) partial pressure of 50 Pa]. This corresponds directly to a decrease of the P-dimer concentration on the surface. Below 620 °C, the degree of order decreases as the growth temperature decreases, even though the concentration of P dimers increases. This is most likely due to the slow migration of adatoms on the surface during growth. The degree of order is found to decrease monotonically with decreasing V/III ratio in the range from 160 to 8 at 670 °C. This corresponds directly to the decrease of the P-dimer concentration on the surface. The direct correlation of the [1̄10]-oriented phosphorus dimer concentration and the degree of order with changes in both temperature (≥620 °C) and V/III ratio suggests that the (2×4) surface reconstruction is necessary to form the Cu–Pt structure, in agreement with published theoretical studies. The physical structure of the surface of these Ga0.5In0.5P layers was also characterized, using atomic force microscopy. For growth at 670 °C and a V/III ratio of 160, the structure of the layers growth on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (approximately 6 Å) steps. As the V/III ratio is reduced, the step height transforms to one monolayer. Exclusively monolayer steps are formed at a V/III ratio of 8. This is interpreted in terms of the stabilization of the bilayers by formation of the (2×2) reconstruction on the (111)B step face at high V/III ratios.

Photoluminescence from GaInP layers and GaInP/AlGaInP quantum wells grown by molecular beam epitaxy with varying growth temperature, phosphorus gas pressure, and substrate orientation

“…Here, E g ð0Þ of fully disordered Ga 0.51 In 0.49 P is taken to be 2007 meV at the absolute zero [18] and 2005 meV at 20 K [19]. Theoretically, DE g ¼ E g ð0Þ À E g ð1Þ is 490 meV [18], which is consistent with experimental DE g E471 meV at 20 K [19].…”

“…The degree of alloy ordering, expressed in terms of a mean order parameter Z; can be estimated from low-temperature PL data [17][18][19][20]. For perfect substitutional randomness Z is zero and for perfect (Cu-Pt type) long-range order Z ¼ 1: The bandgap shrinkage E g ð0Þ À E g ðZÞ and Z are related to each other: E g ðZÞ ¼ E g ð0Þ À Z 2 ½E g ð0Þ À E g ð1Þ:…”

Surfactant effects of dopants on ordering in GaInP

“…3,4 Although the driving force for ordering is understood, the mechanism remains unknown; however, several speculative models have been proposed. 5 Besides the known role of surface reconstruction, surface steps may also be important factors in the ordering process.…”

Growth of order/disorder heterostructures in GaInP using a variation in V/III ratio

“…[8][9][10] Thus, in principle, a much more attractive approach would be to change the flow rate of the phosphorus precursor to produce the desired change in order parameter, although the changes in bandgap energy are typically considerably smaller than for changes in temperature. The initial attempts to produce heterostructures in this way used PH 3 as the P precursor at a growth temperature of 620°C.…”

“…6 This has been demonstrated by the recent experimental observation, using surface photo absorption (SPA), that the concentration of 110 [ ] P-dimers on the (001) surface correlates closely with the degree of order (S) produced during OMVPE growth as the growth temperature and partial pressure of the P precursor (P P ) are varied. [7][8][9][10] It has been suggested that the step structure on the surface during growth may also play a role in the ordering process. [10][11][12] (Received March 13, 1997; accepted May 6, 1997)…”