Abrupt InGaP∕GaAs heterointerface grown by optimized gas-switching sequence in metal organic vapor phase epitaxy

Abstract

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Precise structure control of GaAs/InGaP hetero-interfaces using metal organic vapor phase epitaxy and its abruptness analyzed by STEM

“…We previously developed an optimized gas-switching sequence to fabricate InGaP/GaAs hetero-structures with abrupt hetero-interfaces by MOVPE [17][18][19][20][21][22][23][24]. Two major issues exist in the fabrication of InGaP on GaAs (InGaP/GaAs) hetero-interfaces, which are listed as follows.…”

“…For the case of InGaP layer formation, we introduced the flow modulation sequence to prevent In surface segregation, and the effect of this sequence was confirmed by surface kinetics simulation. We then quantitatively evaluated the abruptness of these hetero-interfaces by using a recently developed technique in which the Z-contrast method is introduced into scanning transmission electron microscopy (STEM) [23,[25][26][27]. The Z-contrast method revealed the optimal gasswitching sequence to realized abrupt hetero-interfaces.…”

“…The most critical problem in GaAs/InGaP hetero-interface fabrication, however, is In segregation, which occurs due to excess In atoms in the top surface of InGaP during growth. During InGaP growth by MOVPE, an In segregation layer can exceed 10 mono-layers (MLs) [22][23][24], and thus causes the degradation of device properties such as effective carrier mobility due to scattering at the interface. We previously developed the ''subsurface'' model that explains In segregation, and has been proven experimentally [19,22].…”

CL and dark field TEM analysis of composition change at interfaces in InGaP/GaAs junctions grown by MOCVD

“…They both suggest that at the inverted GaAs-on-InGaP interface there is the formation of an extra quaternary layer of InGaAsP inside and replacing the nominal GaAs QW layer as suggested in several works [5,10,[15][16][17]. The formation of just InGaAs as sublayer 1 might be less likely because it might easily happen that residual P atoms, remained in the reactor after the PH 3 flow had been switched off, are incorporated in the first monolayers of the GaAs QW since Ga prefers to bond to P rather than to As [18], as far as P atoms are available.…”

“…The stoichiometry of the sublayers 1 and 2 as determined by TEM indicates a slight In and P enrichment of the nominal GaAs QW that thus changes its nature. Such enrichment should be caused by P/As intermixing at the inverted interface and In segregation in the growth direction as discussed elsewhere [5,10,[15][16][17]. TEM further shows the fine structure of the modified nominal GaAs QW, i.e., the presence of two sublayers, one more In and P rich closer to the undergrown InGaP layer and a second one less In and P rich far from it.…”