Metalorganic chemical vapor deposition growth and characterization of InGaP/GaAs superlattices

Abstract

Lattice-matched In 0.49 Ga 0.51 P/GaAs superlattices were grown on (001) GaAs substrates using metalorganic chemical vapor deposition. The interface properties were characterized by photoluminescence, transmission electron microscopy, and x-ray diffraction. By varying the growth temperature, the precursor flow rates, and the growth interruption at the interfaces, we found that, while arsenic and phosphorus carry over have some effect on the formation of a lowbandgap InGaAsP quaternary layer at the interfaces, the In surface segregation seems to play an important role in the formation of the interface quaternary layer. Evidence of this indium segregation comes from x-ray and photoluminescence studies of samples grown at different temperatures. These studies show that the formation of an interfacial layer is more prominent when the growth temperature is higher. Growing a thin (;1 monolayer thick) GaP intentional interfacial layer on top of the InGaP before the growth of the GaAs layer at the P!As transition effectively suppresses the formation of the low-bandgap unintentional interface layer. On the other hand, the growth of a thin GaAsP (or GaP) layer before the growth of the InGaP layer, at the As!P transition increases the formation of a low-bandgap interfacial layer. This nonequivalent effect of a GaP layer at the two interfaces on the PL properties is discussed.

Structural and optical characterization of MOVPE grown InGaP/GaAs MQWs for advanced photovoltaic devices

“…As it is shown in Fig. 2, in both cases the sharpness of the interface degrades with respect to sample 2, in fact, low-energy peaks appears again in the PL spectrum of samples 13 and 14, also in this case attributable to the formation of an undesired quaternary alloy [21]. In addition, the main emission peak, detected, as expected, at about 1.535 eV in samples 13 and 2, shifts toward higher energies (1.557 eV) in sample 14.…”

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

“…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.…”

“…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.…”

“…For MOVPE grown InGaP/GaAs it has been shown by PL, X-ray diffraction and TEM that it is difficult to grow abrupt interfaces between InGaP and GaAs because there is no common group V element across the interface [5]. This especially affects the inverted GaAs-on-InGaP interface where an unwanted extra interlayer forms which recombines the minority carriers more efficiently than the GaAs quantum well [5]. By using cathodoluminescence (CL) in previous works a comparison was made between two InGaP/GaAs based epitaxial systems containing a GaAs QW [6,7].…”

Evaluation of the composition of the interlayer at the inverted interface in InGaP/GaAs heterojunctions

“…InGaP/GaAs has a low conduction band offset that makes it very suitable for HBTs [9]. However, the InGaP/GaAs system has the drawback that an extra interlayer spontaneously forms at the GaAs-on-InGaP interface (inverted interface) [7][8][9][10][12][13][14][15][16][17][18][19][20][21]. The causes suggested in the literature for its formation are three: In carry-over, As/P exchange and P/As intermixing at the location of the inverted interface [7][8][9][10][12][13][14][15][16][17][18][19][20][21].…”