Nanooptics and photonics

A new technique for diagnosing the optical properties of deeply lying epitaxial layers in multilayer nanostructures.
Komarov A.V. 1, Voitovych G.T. 2, Stratiychuk I.B. 3,  Tereshchenko A.G.1, Belevskii P.A1.

1 Institute of Physics of NASU, 03028 Kyiv, Pr. Nauky 46, Ukraine
E-mail of corresponding author: a.v.komarov@i.ua
2 Institute of Physics PAS, 02-668 Warsaw, Al. Lotników 32/46, Poland
3 Institute of Semiconductor Physics of NASU, 03028 Kyiv, Pr. Nauky 41, Ukraine

The paper presents the results of a study of the photoluminescence (PL) spectra of a 305B1 sample of the Cd1-YMgYTe/Cd1-X MnXTe heterostructure (Y = 0.2, X = 0.014), which was grown using molecular beam epitaxy (MBE) technology, and 3 more samples: 305B2, 305B3, 305B4. Samples 305B2, 305B3, 305B4 were made by us using a new technique of the chemical removal of the epitaxial layers Cd0,8Mg0.2Te and Cd0,86Mn0.014Te from the initial sample 305B1 of the said structure.
The aim of this work is to study how the initial shape of the photoluminescence spectrum of a 305B1 structure is transformed after removing from this structure pre-selected regions of width L(1-2) = 550 Å, L(2-3) = 1270 Å, L(3-4) = 4700 Å in samples 305B2, 305B3, 305B4, respectively.
The main tasks of the work: 1) to determine from the results of experimental measurements the spectral characteristics of all resonance PL bands observed in each of the 4 studied samples; 2) according to the obtained experimental data, to establish how the effect of removing epitaxial layers from the studied structures changes the overall picture of the PL spectra.
The PL spectrum of the 305B1 structure consists of four single resonance bands with peaks at E1 = 1.7992, E2 = 1.7257, E3 = 1.6596, E4 = 1.6059 eV and a higher-energy doublet with peaks at E1* = 1.9609, E2* = 1.9399 eV. According to the results of previous studies, single bands are formed by 4 bands of 2D‑excitons, which are localized in four QWs with a width: L1 = 19, L2 = 32, L3 = 58, L4 = 300 Å. A higher-energy doublet band with maxima at E1* = 1.9609, E2* = 1.9353 eV is formed by free excitons in the Cd0.8Mg0.2Te coating layer (LCup = 500 Å). To fabricate the 305B2 structure, the following were removed from the initial 305B1 structure: 1) a coating layer of Cd0.8Mg0.2Te (LCup = 500 Å); 2) the first layer of the Cd1-xMnxTe (L1 = 19 A), responsible for the formation of the 1st QW; 3) a section of width ΔL1B2*=30 ± 20 A of the 1st barrier layer Cd0.8Mg0.2Te (L1B2bar=L1bar - ΔL1B2*=270 ± 20 A). As a result of the removal in the spectrum of 305В2 structure, three bands of 2D‑excitons were detected. The resonance energies of these bands are characterized by the following values: E1, B2 = E2, B1 = 1.7257±0.0001, E2, B2 = E3, B1 = 1.6596 ± 0.0001, E3, B2 = E4, B1 = 1.6059 ± 0.0001 eV. A wide band appeared in the spectrum of the 305B2 sample in the energy range from E = 2.03 to E = 2.4 eV, formed by the intracenter PL of Mn ions in the epitaxial layers of the Cd0.86Mn0.014Te. To fabricate the 305B3 structure, all three layers of the Cd1-xMnxTe (L1, B2 = L2 = 32, L2, B2 = L3 = 58, L3, B2 = L4 = 300 Å) were removed from the initial 305B2 structure; therefore, in the PL spectrum of sample 305B3 the bands of 2D‑excitons observed in the initial spectrum of sample 305B2 were not recorded. In the energy range where three 2D‑excitons bands of sample 305B2 were located, a wide doublet PL band was recorded in sample 305B3, the appearance of which can be interpreted as a manifestation of the intracenter PL of Mn ions located in a thin near-surface region of the Cd0.8Mg0.2Te (L1В3Cup = L1B3* = 5000 Å). This was due to the thermal diffusion of Mn ions at the boundary between the adjacent layers of Cd1-xMnxTe and Cd0.8Mg0.2Te, when for a long period of time (3-5 hours) the studied structure was under conditions of its high-temperature (Т=300о-500о С) growth process using MBE technology. The change in the PL spectrum of sample 305B4 compared to the spectrum of the initial sample 305B3 occurred due to the removal of a wide (ΔLВ4*=4700 А) portion of the Cd0.8Mg0.2Te (L1В3Cup=L1В3*=5000 Å) of sample 305В3. The light wave of laser radiation passes through a thin Cd0.8Mg0.2Te coating layer (L1В4Cup=L1В3*- ΔLВ4*=300 Å) of sample 305В4 and excites free excitons in the CdTe buffer layer (L2Buf = 7 μm), which is located between the Cd0.8Mg0.2Te (L1В4Cup) coating layer and a crystalline substrate in the 305B4 sample. The absence in the sample 305B4 all broad PL bands observed in samples 305B1, 305B2, and 305B3 is associated with the absence of Mn ions embedded in its Cd0.8Mg0.2Te (L1В4Cup) coating layer.