S. Hiyamizu

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.

LATERAL VARIATION OF INDIUM CONTENT IN INGAAS GROWN ON GAAS CHANNELED SUBSTRATES BY MOLECULAR BEAM EPITAXY

Lateral variation of In content in a 1.5 μm thick InxGa1−xAs (x≂0.2) epilayer grown on channeled GaAs (100) substrates having (755)A or (411)A slope regions by molecular beam epitaxy (MBE) was studied by the energy dispersive x‐ray spectroscopy, with high spatial resolution (0.6 μm). Significantly peculiar migration of In atoms on the (411)A was observed. Experimental data of this work strongly suggest that In atoms migrate preferentially in one way, that is to say, they migrate much more in the [122] direction than in the opposite [122] direction on the (411)A plane during MBE growth. The migration length of In atoms on the (100) plane was 5 μm when InGaAs was grown at Ts=570u2009°C and V/III=30.

Highly uniform and high optical quality In0.22Ga0.78As/GaAs quantum wires grown on (221)A GaAs substrate by molecular beam epitaxy

We have grown self-organized InGaAs/GaAs quantum wire (QWR) structures on several kinds of (nnl)A and (nnl)B GaAs substrates by molecular beam epitaxy to optimize the substrate orientation. We observed the most uniform and highest-density corrugation with straight step edges running in the [110] direction on the surface of a 3.0-nm-thick InGaAs layer on the (221)A GaAs substrate among the (nnl)A GaAs substrate. The lateral period of the corrugation was 36 nm and the height was 1.8 nm. On the other hand, GaAs surfaces were almost flat. Hence, a nominally 3.0-nm-thick (221)A InGaAs quantum well sandwiched by GaAs layers is a high density and uniform QWR structure due to the lateral thickness modulation. Photoluminescence (PL) from the (221)A InGaAs/GaAs QWRs structure as 12 K was strongly polarized along the wire direction and its polarization degree P[≡(I∥−I⊥)/(I∥+I⊥)] was 0.20. The PL linewidth was as small as 5.8 meV.

Mobility enhancement by reduced remote impurity scattering in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor structure with (411)A super-flat interfaces grown by molecular-beam epitaxy

We have carried out a Shubnikov–de Haas (SdH) measurement at 4 K and investigated the electronic properties and scattering mechanisms in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor (QW-HEMT) structure with a thin spacer thickness of 3 nm grown on a (411)A-oriented InP substrate by molecular-beam epitaxy (MBE). Electrons occupied the zeroth and first subbands in the 12-nm-thick In0.7Ga0.3As channel layer at two-dimensional electron gas (2DEG) densities of 3.10×1012 and 0.99×1012 cm−2, respectively. 2DEG mobilities of the (411)A sample for the zeroth and first subbands were μ0=52u200a000 and μ1=66u200a000 cm2/Vu200as, which were much higher than those of the (100) QW-HEMT structure (μ0=22u200a000 and μ1=26u200a000 cm2/Vu200as). The result indicates that the electron mobility of the (411)A sample is enhanced by reduction of remote impurity scattering because the spacer thickness (Lsp=3 nm) and distribution of sheet doped impurities are laterally uniform in the (411)A In0.7Ga0.3As/In0.5...

Surface migration of group V atoms in GaAsP grown on GaAs channeled substrates by molecular beam epitaxy

Surface migration of group V atoms (As and P) during molecular beam epitaxy was investigated for the first time by measuring lateral profiles of phosphorus content in GaAsP layers grown on (100)u200aGaAs channeled substrates (CSs) with 12–16 μm wide (n11)A side-slope facet region (n=3, 4, and 5) using As4 and P2 beams. The P content (x) of the GaAs1−xPx layer on the (411)A side-slope region was 43% smaller (x=0.11) than that on the (411)A flat substrates, while P contents of GaAsP layers on (311)A and (511)A side-slope regions were larger than those of GaAsP layers on a corresponding flat substrate. The observed lateral P content profile was well reproduced by simulation based on a conventional surface migration model. The migration lengths of As atoms, LAs, were determined as LAs(411)A=18u200aμm, LAs(100)=28u200aμm, LAs(511)A=33u200aμm, and LAs(311)A=35u200aμm, by comparing the observed and simulated profiles.

Interface roughness characterization by electron mobility of pseudomorphic In0.74Ga0.26As∕In0.52Al0.48As modulation-doped quantum wells grown on (411)A InP substrates by molecular beam epitaxy

Interface roughness of pseudomorphic In0.74Ga0.26As∕In0.52Al0.48As modulation-doped quantum wells (MD-QWs) grown on the (411)A and (100) InP substrates by molecular beam epitaxy was characterized by sheet electron concentration (Ns) dependence of two-dimensional electron gas (2DEG) mobility by applying gate bias at 15K. The (411)A MD-QW with well width of 4nm (8nm) showed value of 1.8–2.1 (1.5–1.6) times higher 2DEG mobility at 15K comparing to the corresponding (100) sample in the range of Ns (1.2–2.3×1012cm−2), which results from reduced interface roughness scattering due to the super-flat (411)A InGaAs∕InAlAs interfaces. By analyzing Ns dependence of the 2DEG mobility, we deduced wave-number dependence of the Fourier components of the lateral well-width fluctuation (Δq0) arising from the interface roughness in the range of q0=0.55–0.7nm−1. Values of ∣Δq0∣2 of the (411)A InGaAs∕InAlAs interface were about half of those of the (100) interface in the whole range of q0=0.55–0.7nm−1.

Improved cathodoluminescence properties of GaAs/Al0.3Ga0.7As tilted T‐shaped quantum wires fabricated on (111)B facet by glancing‐angle molecular beam epitaxy

GaAs/Al0.3Ga0.7As tilted T‐shaped quantum wires (T‐QWRs) were fabricated by growing Al0.3Ga0.7As/GaAs (well thickness of GaAs Lw=4.4 nm) on a (111)B facet plane that was formed when a GaAs/Al0.3Ga0.7As multi‐quantum well (MQW) layer (Lw=4.5 nm) was grown on a reverse‐mesa etched GaAs(100) substrate by glancing‐angle molecular beam epitaxy (GA‐MBE). Growth conditions of the tilted T‐QWR were optimized, and full width at half‐maximum (FWHM) of a cathodoluminescence (CL) peak from the tilted T‐QWRs was reduced down to 19 meV at 78 K, which is about one‐third of that (61 meV) of previous GaAs/Al0.3Ga0.7As tilted T‐QWRs.

Photoluminescence study on twenty GaAs/Al0.3Ga0.7As tilted T-shaped quantum wires fabricated by glancing-angle molecular beam epitaxy

Twenty GaAs/Al0.3Ga0.7Asu2002tilted T-shaped quantum wires (T-QWRs) on a (111)B facet were uniformly fabricated with a two-step growth of molecular beam epitaxy (MBE), which consists of a glancing-angle MBE of GaAs/Al0.3Ga0.7Asu2002multi-quantum well layer with 20 GaAs wells (a well width of Lw=6.1u2002nm) on reverse-mesa stripes on a (001) GaAs substrate and MBE overgrowth of a GaAs/Al0.3Ga0.7As single-quantum well with Lw=6.3u2002nm on a (111)B facet. Full width at half maximum of a photoluminescence peak (λ=792u2002nm) from the tilted T-QWRs was as small as 8.7 meV at 28 K, which is comparable with those (6 meV,Reference 5 10 meVReference 10) of conventional GaAs/Al0.3Ga0.7Asu2002T-QWRs (6.8 nm/5.8 nm, 7 nm/7 nm) fabricated by the cleaved-edge overgrowth.

Room temperature oscillation of self-organized In0.2Ga0.8As/GaAs quantum wire lasers grown on (221)A GaAs substrates by molecular beam epitaxy

Self-organized In0.2Ga0.8As/GaAs quantum wires (QWRs) grown on a (221)A GaAs substrate by molecular beam epitaxy (MBE), which has the narrowest linewidth of photoluminescence peak among self-organized QWRs reported so far, have been applied to an active region of a graded-index separate confinement heterostructure laser structure. Since Si is not a good n-type dopant for (221)A GaAs in the MBE growth, a Sn-doped GaAs/AlAs superlattice layer was used for an n-type cladding layer. The laser operated at room temperature at an emission wavelength of 894 nm under pulsed current conditions with a threshold current of 182 mA (the threshold current density of 2.8 kA/cm2). This result indicates that (221)A InGaAs/GaAs QWRs have sufficient quality for laser devices.

Larger critical thickness determined by photoluminescence measurements in pseudomorphic In0.25Ga0.75As/Al0.32Ga0.68As quantum well grown on (411)A GaAs substrates by molecular beam epitaxy

Pseudomorphic In0.25Ga0.75As/Al0.32Ga0.68As quantum wells (QWs) with well widths (Lw) of 13, 15, 17, 19, 21, and 23 nm were grown simultaneously on the (411)A and (100) GaAs substrates at 480u200a°C by molecular beam epitaxy. The critical thickness of an InGaAs QW layer in the (411)A QW was determined by photoluminescence (PL) measurements at 11 K to be approximately 20 nm, i.e., significant increase in full width at half maximum of PL peaks was observed for Lw⩾20 nm for (411)A QWs. This critical thickness is more than 60% larger than that (around 12 nm) of the (100) QWs.