Growth conditions of metalorganic chemical vapor deposition have been investigated for the purpose of obtaining abrupt InGaP/GaAs interfaces. Photoluminescence (PL) spectra of InGaP/GaAs quantum wells (QWs) are used to characterize these interfaces. The conventional gas switching sequence, i.e., simultaneously switching on group-III and -V gases, is found to provide only a broad peak at wavelengths longer than those of near-band-edge emissions from GaAs in the PL spectrum of the InGaP/GaAs QW. PL studies using QWs having an AlGaAs barrier, for example, AlGaAs/GaAs/InGaP and InGaP/GaAs/AlGaAs, show that the GaAs-on-InGaP interface is responsible for this broad peak. A novel gas switching sequence where group-III gas is switched on first results in sharp peaks corresponding to 5.7- and 2.8-nm-thick wells in the PL spectrum of InGaP/GaAs QW. Preflow of TMGa on InGaP surface is effective in suppressing the substitution of P atoms in InGaP to As atoms at the GaAs-on-InGaP interface.
Non-alloyed ohmic contacts to n-GaAs using compositionally graded In
x
Ga1-x
As layers grown by molecular beam epitaxy are studied. The carrier concentration reduction in the GaAs buffer layer due to low growth temperature is found to increase overall contact resistance for an n+-InAs/In
x
Ga1-x
As(x=1→0)/GaAs structure. The lowest specific contact resistance (ρ
c
) ever reported, 5×10-9 Ω · cm2, is obtained with a 2×1019 cm-3 Si-doped structure grown at 450°C. A similar ρ
c
value is also obtained when the InAs mole fraction is higher than 0.7. Using WSi as a contact metal, a refractory ohmic contact is realized in which ρ
c
remains less than 2×10-7 Ω · cm2 under annealing up to 800°C.
Carrier concentration in very heavily silicon-doped (about 2.7×1019 cm−3) n+-In0.52Ga0.48As epilayer grown on GaAs substrate by metalorganic chemical vapor deposition is decreased by post-growth annealing in the temperature range of 500–800 °C but keeps a value higher than 1.4×1019 cm−3. This value is fairly higher than the reported value for heavily Si-doped GaAs after annealing. It is suggested that the decrease of carrier concentration is not caused by the formation of Si-Si pairs or SiAs acceptors but caused by silicon atom movement from Ga- or In-substitutional sites to interstitial sites at temperatures up to 600 °C and silicon atom outdiffusion at higher temperatures around 800 °C. In less doped (about 5.2×1018 and 1.6×1019 cm−3) samples, a smaller carrier or no decrease is detected after annealing.
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