Fully relaxed low-mismatched InAlAs layer on an InP substrate by using a two step buffer

The strain relaxation in low mismatched InxAl1-xAs layers has been studied by triple axis x-ray diffraction, transmission electron microscopy, and photoluminescence. Using a two step buffer, a fully relaxed top layer has been grown by adapting the composition and thickness of a first "strained layer." The threading dislocation density in the top layer is below 106/cm2 and strain is relaxed at the substrate/first layer interface by misfit dislocations. This scheme is a promising method to limit the thickness of buffer layers and obtain fully relaxed pseudosubstrates

Low-temperature-grown gallium arsenide photoconductors with subpicosecond carrier lifetime and photoresponse reaching 25 mA/W under 1550 nm CW excitation

International audienceThe authors show in this Letter that photoconductors based on GaAs grown at low temperatures can exhibit photoresponses as high as 25 mA/W under continuous-wave 1550-nm-wavelength illumination. It is achieved by using an optical Fabry-Pérot cavity in order to improve the external quantum efficiency and by decreasing the post-growth annealing temperature down-to 450°C. Introduction: Low-temperature-grown GaAs (LT-GaAs) photo-conductors have served as THz sources or detectors in time-domain THz spectroscopy systems based on Ti: Sa mode-locked lasers operating around 800 nm [1]. They have also been used as photoconductive switches to sample millimetre wave signals [2, 3], as optoelectronic homodyne mixers in CW THz spectroscopy systems [4] and also as optoelectronic heterodyne mixers in THz detectors [5, 6]. We have recently shown that LT-GaAs ultrafast photoconductors can operate at λ = 1550 nm, despite a photon energy E ph ≈ 0.75 eV, i.e. lower than the energy gap of GaAs (E g = 1.42 eV), by placing the LT-GaAs layer inside an optical resonant cavity [7]. This photoconductor has been then successfully used to sub-sample continuous waves at frequencies up to 300 GHz, demonstrating a sub-picosecond response time of photocurrents generated by 1550 nm illumination [8]. However, the much higher dark resistivity of LT-GaAs material (>10 3 kΩ cm) in comparison with LT-InGaAs/InAlAs multilayers material [9] or Fe-doped InGaAs layers [10] (<2 kΩ cm) employed in 1550-nm ultrafast photo-conductors is far from compensating the low photoresponse despite the use of an optical cavity (≈ 1 mA/W under CW illumination [7]). These first results have been obtained by using an LT-GaAs layer grown at a temperature of 250 ± 5°C and annealed at 580°C during 60 s. The post-grown annealing is performed in order to decrease the number of point defects (As Ga , As i , V Ga) related to the incorporation of excess arsenic in the layer by forming As clusters. It has been demonstrated several times that it leads mainly to a higher dark resistivity, a lower sub-bandgap absorption [11] and a slight increase of the carrier-lifetime. In this Letter, we show that a photoresponse under CW illumination reaching 25 mA/W can be achieved by decreasing the post-growth annealing temperature down to 450°C. This is 25% of the value obtained using the same type of resonant-cavity-enhanced LT-GaAs photoconductor under 800-nm-wavelength illumination. Under this condition, a dark resistivity of 200 kΩ cm has been measured, which is still two orders of magnitude greater than that of best InGaAs-based ultrafast photoconductive materials [10]. In addition, a clear dependence of the photoresponse and dark resistivity on the post-annealing temperature is shown in the temperature range 450-580°C

Buffer free InGaAs quantum well and in-plane nanostructures on InP grown by atomic hydrogen assisted MBE

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