Yasunori Okamoto

Extremely Flat Interfaces in GaAs/AlGaAs Quantum Wells Grown on GaAs (411)A Substrates by Molecular Beam Epitaxy

GaAs/Al0.3Ga0.7As quantum wells (QWs) grown on (411)A-oriented GaAs substrates by molecular beam epitaxy (MBE) showed extremely flat interfaces over a macroscopic area (about 200 µm ) even for the case of no growth interruption, which is mainly due to the intrinsically large migration of Ga atoms and layer growth in the step-flow mode on the (411)A plane. Photoluminescence linewidths at 4.2K were almost the same as or better than the narrowest linewidths reported for GaAs/AlGaAs and GaAs/AlAs QWs grown on GaAs (100) substrates with growth interruption at each GaAs/AlGaAs(AlAs) interface. Only one sharp luminescence peak was observed for each QW on the (411)A substrates, in contrast with three luminescence peaks for the QWs on the (100) substrates, indicating that extremely flat and uniform interfaces over a macroscopic area of laser excitation (200 µm diameter) are realized in the GaAs/AlGaAs QWs grown on (411)A GaAs substrates.

High-density GaAs/AlAs quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

GaAs/AlAs quantum wires (QWRs) were found to be naturally formed by a regularly corrugated AlAs/GaAs interface and a flat GaAs/AlAs interface in an AlAs/GaAs/AlAs quantum well with a well width of 3.3 nm grown on a (775)B GaAs substrate by molecular beam epitaxy. The lateral period and vertical amplitude of the AlAs/GaAs interface corrugation were 12 nm and 1.2 nm, respectively. The QWRs were formed side by side with an extremely high density of 8×105 QWRs/cm. A photoluminescence peak at λ=715 nm from the QWRs with a cross section of about 12×3 nm2 showed a polarization degree of (I∥ - I⊥) / (I∥ + I⊥) = 0.11 and a very small full width at half maximum of 15 meV at 4.2 K.

Extremely high uniformity of interfaces in GaAs/AlGaAs quantum wells grown on (411)A GaAs substrates by molecular beam epitaxy

GaAs/AlGaAs quantum wells (QWs) were grown on (411)A‐oriented GaAs substrates by molecular beam epitaxy (MBE). Photoluminescence linewidths at 4.2 K are almost the same as the narrowest linewidths reported so far for GaAs/AlGaAs QWs grown on (100)‐oriented GaAs substrates with the growth interruption at the heterointerfaces. Furthermore, only one sharp peak was observed for each QW on the (411) substrate over the whole area of the wafer (10 mm×10 mm), in contrast with three splitted luminescence peaks for one kind of GaAs/AlGaAs QW grown on the (100) substrates by MBE with growth interruption. This result implies that effectively atomically flat interfaces over a macroscopic area (about 10 mm×10 mm) has been realized for the first time in GaAs/Al0.3Ga0.7As QWs grown on (411)A GaAs substrates by MBE. This is possibly due to the large migration of Ga and Al atoms on the (411)A plane during MBE growth and the step‐flow growth mode on the atomically corrugated (411)A plane.

Extremely flat interfaces in InxGa1-xAs/Al0.3Ga0.7As quantum wells grown on (411)A GaAs substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (super-flat interfaces) have been achieved in pseudomorphic In x Ga 1-x As/Al 0.3 Ga 0.7 As (x = 0.0, 0.04, 0.07) quantum wells (QWs) with well widths (L w ) of 1.2-11.8 nm grown on (411)A GaAs substrates at 520°C by molecular beam epitaxy (MBE). A single, sharp photoluminescence (PL) peak was observed for each QW over the large area of the wafer (8 mm x 5 mm). The linewidths for narrow QWs (L w = 2.4nm) were 8.9meV (x = 0.04) and 9.9 meV (x = 0.07) at 4.2 K, which were about 30% smaller than those of QWs simultaneously grown on conventional (100) GaAs substrates.

Extremely flat interfaces in GaAs/AlGaAs quantum wells with high Al content (0.7) grown on GaAs (411)A substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (200 μm diameter) have been achieved in GaAs/Al 0.7 Ga 0.3 As quantum wells (QWs) with well widths of 3.6-12 nm grown on (411)A GaAs substrates by molecular beam epitaxy (MBE) for the first time. A single and very narrow photoluminescence peak (FWHM, full width at half maximum, is 6.1 meV) was observed at 717.4 nm for the QW with a well width of 3.6 nm at 4.2 K. The linewidth is comparable to that of growth-interrupted QWs grown on (100)-oriented GaAs substrates by MBE. A 1.5 μm thick Al 0.7 Ga 0.3 As layer with good surface morphology also could be grown on (411)A GaAs substrates in the entire growth temperature region of 580-700 o C, while rough surfaces were observed in Al 0.7 Ga 0.3 As layers simultaneously grown on (100)GaAs substrates at 640-700 o C. These results indicate that the surface of GaAs and Al 0.7 Ga 0.3 As grown on the (411)A GaAs substrates are extremely flat and stable on the (411)A plane

Much improved interfaces in GaAs/AlAs quantum wells grown on (411)A GaAs substrates by molecular‐beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (200 μm o/) have been achieved in GaAs/AlAs quantum wells (QWs) with well widths of 4.8 to 12 nm grown on (411)A GaAs substrates by molecular‐beam epitaxy (MBE). A single and very narrow photoluminescence peak (FWHM)=7.7 meV) was observed at 742.6 nm for the QW with a well width of 4.8 nm at 77 K. The linewidth is comparable to that of growth‐interrupted QWs grown on (100)‐oriented GaAs substrates by MBE. These results indicate that the surface of GaAs and AlAs grown on the (411)A GaAs substrates are extremely flat and stable on the (411)A plane.

Super-Flat Interfaces in Pseudomorphic InxGa1-xAs/Al0.28Ga0.72As Quantum Wells with High In Content (x = 0.15) Grown on (411)A GaAs Substrates by Molecular Beam Epitaxy

Pseudomorphic InxGa1-xAs/Al0.28Ga0.72As (x = 0.085–0.15) quantum wells (QWs) with well widths of 1.2, 2.4, 3.6, 4.8, 7.2 and 12 nm have been grown on (411)A and (100) GaAs substrates at a temperature (Ts) of 520°C by molecular beam epitaxy (MBE). The interface flatness of the QWs was characterized by photoluminescence (PL) at 4.2 K. PL linewidths of the narrow (411)A QWs (Lw = 2.4 nm) with x = 0.085 and 0.15 were 7.3 meV which is approximately 30–40% smaller than those of the (100) QWs, indicating that extremely flat interfaces over a macroscopic area [(411)A super-flat interfaces] have been realized in the pseudomorphic InxGa1-xAs/Al0.28Ga0.72As QWs (up to x = 0.15) grown on the (411)A GaAs substrates, similar to lattice-matched GaAs/AlxGa1-xAs QWs grown on (411)A GaAs substrate previously reported.