Y.B. Miao

The effects of Si doping in In0.52Al0.48As layers grown lattice matched on InP substrates

The characteristics of Si‐doped In0.52Al0.48As layers as a function of silicon doping ranging from 1×1017 to 4×1018 cm−3 are analyzed by low‐temperature photoluminescence (PL), Raman spectroscopy, and Hall effect measurements. When the sample temperature is increased from 4 K, the PL peak energy exhibits an inverted S‐shaped dependence which is characteristic of carrier localization. This effect was more prominent at lower doping levels, but weakened at high doping levels due to a possible reduction in the donor binding energy. The peak energy variation at temperatures higher than ≊100 K follows the usual band‐edge variation with temperature, suggesting that the PL arises from band‐to‐band transitions. While the PL linewidth of the undoped and moderately doped samples decreases and then increases with temperature, a near‐monotonic increase in the linewidth due to thermal broadening was observed in highly doped samples. Supported by observations of a reduction in both the AlAs‐like and InAs‐like longitudinal‐optic (LO) phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased, the PL intensity also showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.The characteristics of Si‐doped In0.52Al0.48As layers as a function of silicon doping ranging from 1×1017 to 4×1018 cm−3 are analyzed by low‐temperature photoluminescence (PL), Raman spectroscopy, and Hall effect measurements. When the sample temperature is increased from 4 K, the PL peak energy exhibits an inverted S‐shaped dependence which is characteristic of carrier localization. This effect was more prominent at lower doping levels, but weakened at high doping levels due to a possible reduction in the donor binding energy. The peak energy variation at temperatures higher than ≊100 K follows the usual band‐edge variation with temperature, suggesting that the PL arises from band‐to‐band transitions. While the PL linewidth of the undoped and moderately doped samples decreases and then increases with temperature, a near‐monotonic increase in the linewidth due to thermal broadening was observed in highly doped samples. Supported by observations of a reduction in both the AlAs‐like and InAs‐like longitudin...

Effects of substrate temperature and V/III flux ratio on the growth of InAIAs on InP substrates by molecular beam epitaxy

Abstract Molecular beam epitaxial growth of In 0.52 Al 0.48 As epilayers on InP(100) substrates at a wide range of substrate temperatures (470–550°C) and at arsenic overpressures (V/III ratio) which are higher than previously reported [4] is carried out. Analysis performed using low temperature photoluminescence (PL) showed a strong dependence of the photoluminescence (PL) linewidth on the substrate temperature. Corresponding X-ray diffraction measurements showed the lowest lattice-mismatch between the In 0.52 Al 0.48 As epilayer and InP substrate to occur at the substrate temperature at which the lowest PL linewidth was achieved. However, within the range of V/III flux ratios investigated (32 to 266), narrow PL linewidths of less than 20 meV were measured, and the linewidths tend to be generally narrower at flux ratios greater than 150. The lowest value of 14 meV was recorded for the samples grown at a V/III ratio of 160. The lattice-mismatch between the epilayer and the substrate for these samples was also found to be relatively insensitive towards changes in the V/III flux ratios.

Some effects of indium composition on pseudomorphic InxGa1 − xAsIn0.52Al0.48As modulation-doped heterostructures grown by molecular beam epitaxy

Pseudomorphic InxGa1 − xAsIn0.52Al0.48As modulation-doped heterostructures were grown by molecular beam epitaxy (MBE) on InP(100) substrates over a range of indium compositions from x = 0.53 to 0.75. Low temperature photoluminescence (PL) measurements show a prominent reduction in the InGaAs linewidth due to the quantum-size effect as the indium composition is increased from its lattice-match value of 0.53. The lowest linewidth of 6.8 meV was achieved at an indium composition of 0.65, above which an increase in the linewidth was observed due to the overwhelming effects of interfacial strain. The Hall mobilities at 300 and 77 K increase in correspondence to the PL linewidth reduction as the indium composition is increased. Although initial signs of mobility saturation can be seen at an indium composition of 0.65, the peak mobility at 77 K of 8.9 × 104cm2/V · s was achieved at an indium composition of 0.70. There is experimental evidence to indicate that the mobility enhancement at increasing indium composition is due to an effect of a reduction in the alloy scattering and in the effective mass of the carriers. It was found that the insertion of an additional In0.53Ga0.47As interface-smoothing layer between the strained InGaAs channel and the In0.52Al0.48As spacer layer did not have a significant effect on the mobility enhancement in the heterostructures.

Some characteristics of silicon-doped In0.52Al0.48As grown lattice-matched on InP substrates by molecular beam epitaxy

Abstract The characteristics of Si-doped In 0.52 Al 0.48 As layers as a function of the silicon doping are analyzed by low-temperature photoluminescence (PL), Raman spectroscopy and Hall effect measurements. Analysis of the PL intensity at increasing silicon doping levels showed a temperature dependence which is characteristic of disordered and amorphous materials, suggesting a behaviour which has the characteristic of disordered materials at higher doping levels. The PL linewidth broadens at higher silicon doping levels while the Raman scattering spectra showed a reduction in both the AlAs-like and InAs-like longitudinal-optic (LO) phonon frequencies coupled with a broadening of the LO phonon line shape as the doping level is increased.

Silicon doping in In0.52Al0.48As layers grown by molecular beam epitaxy: characterization of material properties

Abstract In 0.52 Al 0.48 As layers at different silicon doping levels are analysed by low temperature photoluminescence (PL), Raman spectroscopy and Hall effect measurements. The PL peak energy exhibits a horizontal S-shaped dependence at increasing temperature, an effect which is more prominent at lower doping levels but weakened owing to a possible reduction in the donor activation energy at higher doping levels. The frequencies of both the AlAs-like and the InAs-like longitudinal optic (LO) phonon modes decrease and the LO phonon line shape broadens as the doping level is increased. The PL intensity also showed in increasing degree, at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials. The temperature dependence of the Hall mobility exhibits clear contributions μ i and μ po from ionized impurity and polar optical phonon scattering at low and high temperatures respectively in the samples with low and moderate doping levels. Our data suggest a solubility limit of about 8 x 10 18 cm −3 for silicon doping in the InAlAs material.

Optical and structural characterizations for optimized growth of In0.52Al0.48As on InP substrates by molecular beam epitaxy

Abstract Growth of In 0.52 Al 0.48 As epilayers on InP(100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470–550 °C) and at high arsenic beam equivalent pressures is carried out. Analysis performed using low-temperature photoluminescence (PL) and double axis X-ray diffraction (XRD) showed a strong dependence of the PL and XRD linewidths and lattice-mismatch on the substrate temperature, with minimum linewidths and lattice-mismatch occurring between approximately 500 and 520 °C. The XRD intensity ratio (Int epi /Int sub ) varied in opposition to the lattice-mismatch, with higher intensity ratios corresponding to lower lattice-mismatches. From the X-ray diffraction curves of samples grown at low temperatures, it was observed that the main peak associated with the InAlAs epilayer is comprised of smaller peaks, which strongly indicates disordering owing to the presence of alloy clustering. PL spectrum taken at increasing temperatures showed the quenching of the main emission peak followed by the evolution of a distinct peak at lower energy, possibly associated with carrier localization due to the presence of lattice disorder. In addition to the InAs-like and AlAs-like longitudinal-optic (LO) phonon modes at 234 cm −1 and 370 cm −1 , respectively, Raman scattering measurements also showed an additional higher energy mode at 273 cm −1 in the samples grown at lower temperatures approaching 470 °C. Within the range of V/III flux ratios investigated (32–266), the lowest PL linewidth of 14 meV was recorded for the samples grown at a V/III ratio of 160 at a substrate temperature of 510 °C. The lattice-mismatch between the epilayer and the substrate for these samples was also found to be relatively insensitive to changes in the V/III flux ratios.

Molecular beam epitaxial growth of high quality InAlAs on InP (100) substrates at very high arsenic pressures

Abstract We report in this letter the molecular beam epitaxial (MBE) growth of In0.52Al0.48As on InP (100) substrates at very high arsenic overpressures and their characterisation using low temperature photoluminescence (PL) and X-ray diffraction (XRD). The effect of the high arsenic overpressures on the optical quality and lattice-mismatch in the In0.52Al0.48As material were investigated. Within the range of the V/III flux ratios investigated (32–266), our results show for the first time that very high arsenic overpressures during MBE growth have no detrimental effect on the quality of the InAlAs, in contrast to the generally believed crystalline degradation due to the adverse effect on the cation surface mobilities. There is also an insignificant effect on the quality of the heterointerface as the lattice-mismatch was relatively insensitive to flux ratio variations within the range investigated. A significant improvement in the uniformity of the PL peak energy was also observed.

Photoluminescence and Raman scattering characterization of silicon-doped In 0.52 Al 0.48 As grown on InP (100) substrates by molecular beam epitaxy

Growth of In0.52Al0.48As epilayers on InP (100) substrates by molecular beam epitaxy at different silicon doping levels is carried out. The doped samples show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. There is a reduction in both the AlAs-like and InAs-like longitudinal-optic (LO) phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased. The PL intensity also showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.

A photoluminescence and X-ray diffraction analysis of InAlAs/InP heterostructures grown by molecular beam epitaxy

Abstract Growth of In 0.52 Al 0.48 As epilayers on InP(100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470–550 °C) and at arsenic beam equivalent pressures which are higher than previously reported (D.F. Welch et al., Appl. Phys. Lett., 46 (1985) 169), is carried out. A strong dependence of the photoluminescence (PL) and X-ray diffraction (XRD) linewidths and XRD intensity ratio (Int epi /Int sub ) on the substrate temperature was observed. The lattice mismatch was the lowest when the growth was carried out at substrate temperatures of 500–520 °C. The XRD diffraction peaks of samples grown at low temperatures are comprised of smaller peaks suggesting an effect of disordering owing to the presence of alloy clustering. PL linewidth as low as 14 meV was recorded in samples grown at a V/III flux ratio as high as 160. The lattice mismatch in samples grown at high flux ratios was found to be insensitive to changes in the V/III flux ratios.

Photoluminescence characteristics of Si-doped In0.52Al0.48As grown on InP substrates by molecular beam epitaxy

The photoluminescence (PL) characteristics of Si-doped In0.52Al0.48As layers as a function of temperature and silicon doping level ranging from 1 × 1017 to 4 × 1018 cm−3 are reported. When the sample temperature is increased from 4 K, the PL peak energy exhibits an inverted S-shaped dependence which is characteristic of carrier localization. This effect was more prominent at lower doping levels but weakened at high doping levels due to a possible reduction in the donor binding energy. The peak energy variation at temperatures higher than ∼ 100 K follows the usual band-edge variation with temperature suggesting that the PL arises from band-to-band transitions, while at temperatures lower than ∼ 50 K, donor-to-band transitions are probably dominant. The PL linewidth of the undoped and moderately doped samples decreases and then increases with temperature, whereas in the highly doped samples, a near montonic increase in the linewidth due to thermal broadening was observed. In all the samples, the PL intensity showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.