In this work, the influence of the surface depletion layer on the formation of a two-dimensional electron gas in AlGaAs/GaAs modulated doped heterostructures is studied. The authors explore a method for estimating the depletion region inside of the GaAs-based heterostructures by using the longitudinal optical and L- amplitude modes observed in Raman spectra, which are supported by the modeling results. The authors found that the position of the topmost doping layer changes the electron distribution in the heterostructure and decreases the influence of the depletion layer. Similar effects are perceived when an optimized solution of (NH4)2SX and isopropanol is employed. The authors present a method to evaluate the formation of a double two-dimensional electron gas in a heterostructure by the adequate use of modulation line in the photoreflectance spectroscopy.
Laser operation at room temperature of self-organized In 0.1 Ga 0.9 As/(GaAs) 6 (AlAs) 1 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxyThe authors report a low-temperature photoluminescence (PL) study of multiple GaAs layers grown between AlAs(0.6 nm)/GaAs(0.6 nm) short-period superlattice barriers (SLBs) simultaneously grown on both GaAs(631)A and (100) substrates. Five GaAs-layers of different nominal thicknesses (L W , ranging from 12 to 2.4 nm) were grown by molecular beam epitaxy. By using (631)A-oriented substrates a self-organized and highly ordered corrugation is obtained in the growth of the GaAs layers, and at the end of the SLB growth, flat surfaces are found. Whereas, for the (100)-oriented sample, flat interfaces are confirmed after the growth of GaAs and SLB layers. By reducing L W below $3.6 nm in the (631) sample, strong quantum wire (QWR)-like confinement is achieved as deduced from polarized PL spectroscopy where polarization degrees as large as 0.43 are obtained. The PL emission energy of the (631)-QWRs is redshifted, as compared with the transitions of the (100)-oriented quantum wells, when L W is reduced. The authors explain this energy shift by the widening of the effective thickness of the confinement regions in the GaAs layers.
The influence of near surface structure termination and surface treatments on the surface electric fields and mobility of modulation doped AlGaAs/GaAs heterostructures (MDH) were investigated. The built-in and surface electric fields were evaluated by photoreflectance spectroscopy, and these values were utilized to simulate the conduction band bending of the MDH. When the capping layer of the MDH was changed, both the built in internal electric field and the surface electric field are decreased, while the electron mobility of the samples is increased. After passivated the surface samples with Si, the surface electric fields were also reduced. Finally, a (NH4)2Sx-based treatment of the surface was applied, the surface electric field is annulled, and the conduction band modeling showed an important redistribution of carriers in the films. The electron mobility of the passivated samples does not show any change, neither the internal electric fields, corroborating the close relationship that exist between these two parameters.
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