Epitaxial growth of CuGaSe 2 thin-films by MBE—Influence of the Cu/Ga ratio

Abstract

By molecular beam epitaxy (MBE) CuGaSe 2 (CGS) thin-films with varying Cu/Ga ratios were grown epitaxial on GaAs (100) and stepped GaAs (111)A substrates. Cu/Ga ratios from Cu-poor to Cu-rich were obtained. In this work the appearance of Cu crystallites on the surface of epitaxial CGS (001) layers are observed and strategies to avoid these precipitations are presented. High quality thin CGS films of around 100 nm thickness are obtained, enabling a detailed analysis of the electronic and chemical properties as well as of the crystal structure of the CGS surfaces. The electronic structure with respect to the Cu/Ga ratio was characterized in-situ by XPS and UPS. By LEED a (4x1) (Cu-poor and near stoichiometric) and a (4x2) (Cu-rich) reconstruction of a zinc blende structure were obtained. For CuGaSe 2 (112) the LEED pattern showed a (3x1) chalcopyrite reconstruction for Cu/Ga ratios < 1. A (1x1) reconstruction of the chalcopyrite structure was observed for Curich (112) samples. The observed dependence of the surface reconstruction on the stoichiometry for CGS grown on GaAs has not been reported in literature so far. Additionally, for Cu-rich stoichiometries a binary phase of Cu 2-x Se appeared independently of orientation. The film morphology was investigated ex-situ by SEM.

Epitaxial CuGaSe2 Thin Films − Removal of Cu2−xSe Secondary Phase From Film Surface

“…Due to the annealing step a surface reformation takes place, which can also be observed in the crystal structure by using LEED as depicted in Figure . Prior to the annealing step, the Cu‐rich CGS (001) surface shows a (4 × 2) single domain reconstruction of the zinc blende order as expected …”

“…Considering just the main components of the Cu core level and Auger line, α Cu amounts to 1849.4 eV, this can be assigned to Cu‐chalcopyrites (according to the NIST database of X‐ray photoelectron spectroscopy). The Cu Auger parameter changes to 1850.7 eV by taking into account only the shoulder components, which hints to a presence of a Cu 2− x Se secondary phase . This binary phase leads also to a widening of the Auger emission line in Figure b.…”

“…The Cu Auger parameter changes to 1850.7 eV by taking into account only the shoulder components, which hints to a presence of a Cu 2Àx Se secondary phase. [20,21] This binary phase leads also to a widening of the Auger emission line in Figure 3b. However, after annealing the sample for 10 min at 600 C the shoulder components of the Cu core level as well as for the Auger emission line disappear (Figure 3b, c).…”

“…For CGS as a ternary compound semiconductor a wide range of stoichiometries are possible. [20,21] The phase diagram of CGS ( Figure 1) exhibits five possible phases, whereby a coexistence of several phases may be present. A Cu-poor defect compound exists for a copper content under 13%, named b-phase.…”

Atomik Katman Biriktirme Tekniğine Genel Bakış: Zno, Tio2 Ve Al2o3 Filmlerin Üretimi

“…Bu alanlarda üretilen yüksek dielektrik sabitli transistörler [1][2][3][4][5], bellek aygıtları [6][7][8], gaz difüzyon bariyerleri [9][10][11], organik ışık yayan diyotlar (OLED'ler) [12][13][14], esnek elektronik aygıtlar [15], yakıt hücreleri [16][17][18], sensörler [19][20][21], güneş panelleri [22][23][24][25], biyoelektronik cihazlar, implantlar, ilaç sistemleri [26][27][28][29], su ayrıştırma [30][31][32][33] gibi pek çok teknoloji ince film üretim tekniklerinin kullanmasını gerektirmektedir. Magnetron sputtering [34][35][36], moleküler ışın epitaksi (MBE) [37], Spray-pyrolysis [38], sol-gel [39,40], kimyasal buhar biriktirme (CVD) [41,42] ve atomik katman biriktirme (ALD) [43][44][45] gibi fiziksel ve kimyasal yöntemler de dâhil olmak üzere hali hazırda pek çok ince film kaplama ve büyütme teknikleri mevcuttur. Bu üretim teknikleri aras...…”