Evidence of the miniband formation in InGaAs/InP superlattices

Abstract

The formation of the miniband electron energy structure was explored in doped InGaAs/InP superlattices with different periods. The analysis of the Raman data allowed us to conclude that in spite of the defect structure of the layers constituting the superlattices, their super-periodicity was well defined. The quantitative proof of the conditions for break-down of the Raman selection rules is presented: the emergence of the selection rules of the coupled plasmon-LO phonon vibrations was demonstrated to occur due to the increase of their coherence lengths. In addition, the expected anisotropy of the effective electron masses was found by high-field magnetoresistance.Keywords: Superlattices; Plasmons; Raman scattering InGaAs/InP heterostructures present an important class of semiconductor materials with possible applications in infrared optoelectronics. Moreover, a large g-factor found in these materials [1] makes them promising in the field of spintronics and quantum information processing. A manipulation of the electronic properties (including g-factor engineering) important in device applications is possible in superlattices (SLs) -structures consisting of periodic sequences of the layers made of two different semiconductor materials. In such structures the dynamic electron properties can be tuned in the direction perpendicular to the layers by a variation of their thicknesses or compositions. However, to the best of our knowledge until now an evidence of the formation of the superlattice bandstructure in the InGaAs/InP SLs was only recently obtained by high-field magnetotransport in Ref. [2]. The photoluminescence data presented in this reference also indicated the existence of the minibands.In this work we explored the Raman scattering of the coupled plasmon-LO phonon modes propagating perpendicular to the layers of the short-period doped InGaAs/InP SLs. The manifestation of the coupled modes in the short-period SLs was assigned to the formation of the miniband energy structure caused by the SL periodicity. We also found an additional indication of the miniband formation by high-magnetic field magnetoresistance measurements. Moreover, a considerable effect of the super-periodicity on the Raman selection rules of the coupled modes was observed.A total number of 30 periods of the (In 0.53 Ga 0.47 As) m (InP) m SLs with m = 6,8,10,15,and 68 ML (excepting the SL with m = 68 which has 20 periods), where n is the thickness of the layers expressed in monolayers (1ML = 2.9 o A), were grown on semi-insulating (001) InP substrates by molecular beam epitaxy. The high-resolution x-ray diffraction showed the variation in the period of our SLs of about 0.3%. The barriers of the SLs were doped by Si in order to form a gas of degenerate electrons with the density determined by the Hall measurements 5.0x10 17 cm −3 . The doping was kept the same for all the SLs reported here.The magnetoresistance measurements were performed on samples patterned into an active area of 4x4 mm. The Ohmic contacts were fabricated by depositing ind...