Spontaneous formation of Al rich and Ga rich AlxGa1−xAs/AlyGa1−yAs superlattice and strong enhancement of optical properties

Abstract

Long range composition ordering and spontaneous formation of Al rich and Ga rich AlxGa1−xAs/AlyGa1−yAs superlattice were demonstrated. This was observed by cross-sectional transmission electron microscopy (TEM) in a 280 Å Al0.4GaAs quantum well laser diode heterostructure with Al0.7GaAs barriers grown on (111)B GaAs substrates. On the contrary, none of above superstructure was observed by TEM on a side-by-side grown (100) oriented substrate. More evidence is shown in the (111)B Al0.7GaAs barriers which were disordered due to a high growth temperature and did not show any superstructure. 10 K photoluminescence was shown with 32 meV redshift and a 12-times peak intensity enhancement in (111)B orientation.

UV absorption characteristics and element composition of (200) and (111) orientation cubic MgZnO thin films deposited at different temperature by PLD method

“…Semiconductor alloy thin films with different orientation may have different characteristics and performance in optical electronic devices. For example, because of the different surface reactions, bonding energy, and migration velocity of group III atoms on (111) orientation from those on (100) surface, the crystal quality of (111) orientation AlGaAs thin film with cubic structure is better than (100) orientation one [21,22], the PL intensity of (111) orientation AlGaAs thin film is much higher than (100) orientation one [23,24]. Similar phenomenon may exist in cubic MgZnO alloy with similar structure as AlGaAs, it has been reported that the crystal quality of (111) orientation MgZnO thin film deposited on lattice mismatched sapphire substrate is nearly the same as (200) one deposited on lattice matched MgO substrate under nearly the same growth conditions by the same method, so crystal quality of (111) orientation MgZnO thin film may be higher than (100) one on the same substrate as AlGaAs thin film, and (111) orientation MgZnO thin film may have sharper UV absorption edge, which is important for its application in effective detecting deep UV light with certain wavelength.…”

Phase Separation in AlxGa1-xAs Nanowhiskers Grown by the Solution−Liquid−Solid Mechanism

“…We now report the results of transmission electron microscopy (TEM), photoluminescence spectroscopy, electron energy loss spectroscopy (EELS), and annealing studies conducted on Al x Ga 1 - x As nanowhiskers grown by a low-temperature, solution-based method. These studies strongly suggest that the Al x Ga 1 - x As nanowhiskers possess phase-separated nanostructures, which are unusual for Al x Ga 1 - x As − and are not predicted by the AlAs−GaAs pseudobinary phase diagram . Phase-separated nanostructures are known to significantly enhance the photoemission behavior of ternary semiconductors.…”

“…In contrast, the thermodynamic miscibility gap in the AlAs−GaAs pseudobinary phase diagram is depressed to very low temperature ( T MG = 64 K), and thus conventionally grown Al x Ga 1 - x As materials are homogeneous alloys (see Figure ). However, spontaneous phase separation in Al x Ga 1 - x As has been observed in films deposited by low-temperature molecular beam epitaxy (MBE) upon specific substrates and substrate orientations. − These films possess lamellar, compositionally modulated nanostructures. The origin of the phase separation has been ascribed to various kinetic and thermodynamic effects operating at the surface or immediate subsurface of the growing films, ,,,,− but remains incompletely understood. , Significantly, the lamellar, phase-separated Al x Ga 1 - x As films exhibit photoluminescence intensities of up to 3 orders of magnitude higher than those of the corresponding homogeneous-alloy films .…”

“…The origin of the phase separation has been ascribed to various kinetic and thermodynamic effects operating at the surface or immediate subsurface of the growing films, ,,,,− but remains incompletely understood. , Significantly, the lamellar, phase-separated Al x Ga 1 - x As films exhibit photoluminescence intensities of up to 3 orders of magnitude higher than those of the corresponding homogeneous-alloy films . As in the In x Ga 1 - x N examples, collection and confinement of carriers in the lower-band-gap regions, in these cases the comparatively Ga-rich layers, enhance radiative recombination. ,, …”

Optical and structural properties of spontaneously formed long-range compositional modulation in (111)A and (111)B AlGaAs

“…Recently, we have reported the first growth induced compositional modulation in ͑111͒B AlGaAs and achieved more than one order of magnitude of enhanced PL intensity, at a low growth temperature of 600°C. [10][11][12] The improved optical property is related to the increased quantum confinement by the compositional modulation. An improved optical property in AlGaAs grown at a relatively low growth temperature of 600°C is greatly desired for AlGaAs, that usually grown on ͑100͒ substrate shows a strong dependence on growth temperature as far as optical properties are concerned.…”