Photoluminescence of InAs quantum dots inn-i-p-iGaAs superlattice

Abstract

Large blueshift and linewidth increase in photoluminescence ͑PL͒ spectra of InAs quantum dots ͑QD's͒ in n-i-p-i GaAs superlattice were observed. By increasing the excitation intensity from 0.5 to 32 W/cm 2 , the PL peak position blueshifted 18 meV, and the linewidth increased by 20 meV. Such large changes are due to the state-filling effects of the QD's resulted from the separation of photogenerated electrons and holes caused by the doping potential.The optical properties of InAs self-assembled quantum dots ͑QD's͒ have been of great interest in recent years. The interband and intraband optical transitions of these QD's are widely studied, both for the interest in fundamental physical properties and for the development of QD lasers and photodetectors. It is important to investigate electron-hole separation effects in QD's and design QD structures that can separate and store photoexcited carriers for memory-device applications. However, few works were done in this field. Recently, Schoenfeld et al.1 have designed a QD device that can separate and store photoexcited electrons and holes. Their structure consisted of two GaAs quantum wells of different thickness, separated by a thin AlAs barrier. An InAs QD layer is inserted in the thick quantum well. The strain these InAs QD's create induces QD's within the thin GaAs quantum well that are coupled to the InAs QD's in the thick well. In their structure, photogenerated electrons and holes are spatially separated into the InAs QD's and strain-induced QD's, respectively.In this work, we study a different QD structure designed to spatially separate and store photogenerated electrons and holes. In this structure, InAs self-assembled QD's were grown in the n-type and p-type regions of a n-i-p-i GaAs superlattice. Photogenerated electrons and holes in GaAs barriers are expected to be swept by the intrinsic electric field to the n-doped regions and the p-doped regions, respectively, and trapped by the InAs QD's there. As the photogenerated electrons and holes fill up the lower QD states, photoluminescence ͑PL͒ properties of these InAs QD's different from conventional QD's inserted in intrinsic GaAs layers are expected. In our PL experiments, large blueshift of the PL peak and increase of the PL linewidth with increasing excitation intensity were observed for the QD's in the n-i-p-i GaAs superlattice, whereas for similar InAs QD's in intrinsic GaAs layers, only a small blueshift of the PL peak and increase of the linewidth were observed. The large blueshift in the n-ip-i QD's is a clear indication of the state filling of the QD's due to electron-hole separation.The samples were grown by molecular-beam epitaxy on a ͑001͒ N ϩ GaAs substrate. After deposition of a 1-m semiinsulating GaAs type buffer layer, 10 periods of n-type GaAs ͑20 nm͒/InAs QD's (2 ML)/n-type GaAs (20 nm)/p-type GaAs ͑20 nm͒/InAs QD's (2 ML)/p-type GaAs ͑20 nm͒ were grown. The n-type regions were Si doped and the p-type regions were Be doped; both n and p doping concentrations are 1ϫ10 18 cm Ϫ3 . The growth t...

Effect of carriers transfer behavior on the optical properties of InAs quantum dots embedded in AlGaAs/GaAs heterojunction

“…In Table I we report the FWHM values of the ground state and the first excited state of ͑S1, S2, and S3͒ samples. 31 Similar behavior is observed by Kumagai et al 32 on InAs/ GaAs QDs with modulation doped ͑p-doped with beryllium͒, they explained the increase in FWHM by the interdiffusion of beryllium atoms from the GaAs to the QDs layer. In fact, when QDs are placed near the channel, they behave like doped-QDs, because doping atoms are supposed to introduce radiative recombination centers which will increase the FWHM.…”

Nuclear matter at finite temperature and static properties of proto-neutron star

“…In several works [14,19,49] that also investigated the finite temperature properties of nuclear matter, the entire interaction involves temperature dependence. However, similar to [3,5,6,18,50,16,9], in [20] the temperature effects were invoked through the kinetic part of the interaction which also successfully explained the finite temperature properties of nuclear matter at low density. In the present work I consider same approach with the same model as [20] to examine the thermal properties of nuclear matter more rigorously at different density domains.…”

“…It is therefore that one rely on theoretical modeling of proto-neutron star matter (PNSM) to understand its composition and compute the EoS on its basis. A lot of work has been done in this regard to comprehend successfully the temperature dependence of nuclear matter properties [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] using a wide variety of approaches. Based on microscopic treatments, two and three body nuclear potentials were constructed using chiral effective theory [24,25] to compute the nuclear matter properties at finite temperature while nuclear dipolar strength was successfully calculated by adopting finite-temperature relativistic time blocking approximation [26].…”

“…It is well-known that nuclear matter properties are best determined at low density mainly around ρ 0 . The phenomenon of liquid-gas phase transition is of great interest in this domain of study [20,51,42,38,52,53,54,55,56,9,10,14,16,17,23]. The isotherms at low density manifest a Van der Waal like interaction indicating the coexistence of both liquid and gaseous phases upto a certain density depending on the temperature.…”

“…This transition temperature is called the critical temperature T c . A lot of experimental endeavors have determined the range of T c to be within (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) MeV [57,58,59,60,61,62,63,9,20]. It is also known that liquid-gas phase transition can also be attained with ANM for low values of the asymmetry parameter α and temperature [16,20].…”