No abstract

Comprehensive studies on the surface morphological evolution of AlInSb metamorphic buffers and InSb QWs grown on top were conducted as a function of the GaAs (001) substrate offcut angles. We confirmed our earlier postulation that the vicinal surfaces defined by the hillock facets have the exact surface orientation needed to achieve large-area hillock-free surfaces. The related morphological transitions were discussed with a graphic illustration. The optimum substrate offcut for InSb towards [110] direction was found to be around 0.5∼0.6 • with our growth conditions. On 2-inch GaAs (001) substrates with this offcut, a hillock-free and atomically smooth surface morphology was successfully achieved for modulation-doped InSb QWs.

The authors compare four methods to investigate the threading dislocations (TDs) observed in metamorphic buffers used in the growth of InSb quantum well on GaAs (001) substrates. Three types of buffers with varying number of Al0.24In0.76Sb interlayers (N = 0, 1, and 3) were studied. Cross-sectional scanning transmission electron microscopy (STEM) revealed an effective dislocation filtering by the interlayers. Individual TDs were identified with atomic-force microscopy (AFM) as distinct morphological features of dislocation outcrops on the surface. Threading dislocation density (TDD) is reduced by 1 order of magnitude with three interlayers, consistent with the STEM observation. TDD measured with a scanning electron microscope in electron channeling contrast imaging (ECCI) mode agrees closely with the AFM analysis, except for the N = 0 buffer where the ECCI gives TDD lower by more than a factor of two. The etch pit density of N = 3 buffer, measured with a Nomarski differential interference contrast microscope after defect selective etching (DSE), is almost 1 order of magnitude lower than the TDD measured by AFM and ECCI. Due to the large pit size, the used etching recipe only works well for samples with TDD lower than 107 cm−2. AFM, ECCI, and DSE are excellent alternatives to transmission electron microscopy in the process of metamorphic buffer optimization. The AFM technique offers the additional advantage of high vertical resolution morphology mapping. Such capability is of great importance for the optimization of metamorphic buffers from the perspective of surface smoothness improvement.

An integrated spectral pyrometry (ISP) technique particularly well suited to monitor the temperature of small bandgap semiconductors during molecular beam epitaxial growth is proposed. The technique relies on integrating the thermal radiation power emitted by the wafer over a spectral range where it is fully opaque, so as to avoid contribution from radiation transmitted from the substrate heater. In the present work, a 900–1700 nm array InGaAs spectrometer normally employed for band-edge thermometry was used. The temperature dependence of the integrated signal can be expressed by an Arrhenius-type exponential relation. The calibration procedure and the method employed to compensate for the background radiation from other hot objects in the reactor is discussed. The ISP performance is then demonstrated by monitoring the temperature during the growths of a Si doped InAs layer on InAs substrate and of an InSb/AlInSb quantum well structure on GaAs substrate. The ISP technique allows reproducible wafer temperature monitoring down to about 200 °C.

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in surface indium antimonide quantum wells. The topmost 5 nm of the 30 nm wide quantum well is doped and shown to promote the formation of reliable, low resistance Ohmic contacts to surface InSb 2DEGs. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 1 in magnetic fields of up to B =  18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinch-off to 4 [Formula: see text] cm−2, and peak mobilities exceed 24 000 cm2/V s. Large Rashba spin–orbit coefficients up to 110 meV [Formula: see text]Å are obtained through weak anti-localization measurements. An effective mass of 0.019 me is determined from temperature-dependent magnetoresistance measurements, and a g-factor of 41 at a density of 3.6 [Formula: see text] cm−2 is obtained from coincidence measurements in tilted magnetic fields. By comparing two heterostructures with and without a delta-doped layer beneath the quantum well, we find that the carrier density is stable with time when doping in the ternary Al0.1In0.9Sb barrier is not present. Finally, the effect of modulation doping on structural asymmetry between the two heterostructures is characterized.