Spatially direct charged exciton photoluminescence in undoped ZnSe∕BeTe type-II quantum wells

Abstract

Photoluminescence (PL) spectra occurred as a spatially direct optical transition inside of the ZnSe layer in undoped ZnSe∕BeTe∕ZnSe type-II quantum structures have been studied. We have found that the charged exciton transition was observed at the lower energy side of the exciton transition in the spatially direct PL. The formation of the charged exciton was attributed to the accumulated electrons in the ZnSe layer after the photoexcitation accompanied by the holes being escaped from this well and injected into the BeTe layer.

Spatially indirect photoluminescence of ZnSe/BeTe type II quantum wells in pulsed high magnetic fields

“…If we assume the electron as a final state, then the charged exciton is a negatively charged exciton denoted by X -, while if the hole is the final state, then the positively charged exciton (X + ) is responsible for the SID PL as an initial state. In our recent paper, a negatively charged exciton transition is reported as a direct transition of PL occurred inside of the ZnSe layer in a similar quantum structure to the present one [2,8]. This is a definite evidence of the existence of free electrons (free from bound states) in the ZnSe layer upon photo excitation.…”

Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells

“…The QWs in the samples consisted of one set (for #237), and three sets (for #288) of symmetrical ZnSe (28 ML) /BeTe (10 ML)/ZnSe (28 ML) layers as described in detail in Refs. [15], [18] and [19], where 1 ML was approximately equal to 0.28 nm. In the n-doped sample, the doped layers (ZnCl 2 ) were separated from the QWs by 10 nm-thick barrier layers as shown in Fig.…”

“…Other parameters of the two samples were identical. [15,18,19] The samples were grown in Ultrafast Photonic Devices Laboratory of AIST in Japan.…”

Type-I interband transition in undoped ZnSe/BeTe type-II quantum wells under high excitation density

“…The QW structures are sandwiched by 200 nm thick Zn 0.77 Mg 0.15 Be 0.08 Se barrier layers. More details about the two samples are described in [11,14]. For the DT-PL measurements, a frequency-doubled mode-locked Ti:sapphire laser is used as an excitation light source.…”

“…The ZnSe/BeTe quantum well structures have a type-II band alignment with large band offsets, namely 2.3 eV for the conduction band and 0.9 eV for the valence band [8][9][10]. In such deep potential wells, photo-excitation in ZnSe layers causes a unique situation where the electrons stay in the same layer, whereas some of the holes escape from the ZnSe layer, and are injected into the next neighbor BeTe layer due to the energy minima for electrons and holes lying in different layers [11][12][13][14][15]. Consequently, the spatial separation of the photoexcited electrons and holes in the ZnSe layer results in free electron accumulation in the ZnSe layer, and enables us to observe the transitions from spatially direct (i.e., type-I) X − within the ZnSe layer [6,11].…”