High n-type Sb dopant activation in Ge-rich poly-Ge1−xSnx layers on SiO2 using pulsed laser annealing in flowing water

Abstract

Heavy n-type doping in polycrystalline Ge (poly-Ge) is still under development owing to the low solid solubility and the low activation ratio of group-V dopants in Ge. To solve this problem, we have investigated ultra-short (55 ns) laser pulse annealing in flowing water for Sb-doped amorphous Ge1−xSnx layers (x ≈ 0.02) on SiO2. It is found that fully melting a Ge1−xSnx layer down to the Ge1−xSnx/SiO2 interface leads to a large grained (∼0.8 μmϕ) growth, resulting in not only a high electrical activation ratio (∼60%) of Sb atoms in the polycrystals but also a high electron density around 1020 cm−3. As a result, the electron mobility in the Ge-rich poly-Ge1−xSnx layers exceeds that in single-crystalline Si even in the region of a high electron density around 1020 cm−3. The low thermal budget process opens up the possibility for developing Ge1−xSnx based devices fabricated on 3D integrated circuits as well as flexible substrates.

Sb-doped crystallization of densified precursor for n-type polycrystalline Ge on an insulator with high carrier mobility

“…[4][5][6][7][8] The most promising usage of such high-performance Ge-CMOS is to integrate it into Si large-scale integrated circuits (LSIs) or flat-panel displays. To achieve this, low-temperature Ge-on-insulator (GOI) technology has been developed, including solid-phase crystallization (SPC), [9][10][11][12][13] laser annealing, [14][15][16][17][18] chemical vapor deposition, 19,20 flash-lamp annealing, 21 the seed layer technique, 22 and metal-induced crystallization. [23][24][25][26][27] Using the resulting polycrystalline (poly-) Ge layers, p/n-channel MOSFETs 12,13,17,21,27 and even CMOS operation have been successfully demonstrated.…”

“…Although n-type doping to poly-Ge in a low thermal budget is challenging because of the low solid solubility of n-type dopants in Ge, 34,35 heavy n-type doping (>10 19 cm À3 ) to Ge thin films has been achieved by short-time annealing techniques. 18,36 These techniques are promising for fabricating source/drain junctions for n-MOSFETs.…”

“…The activation ratio of Sb in Ge was estimated to be approximately 1% in the whole range of C Sb , when not considering the acceptors in poly-Ge. 9,18 The solid solubility limit of Sb in Ge at T g ¼ 450 C is approximately 10 18 cm À3 , 34 which is one reason for such a low activation ratio. Figure 3(c) shows that l n has the same tendency as n in each C Sb : l n attains its maximum value around T d that provides the maximum grain size (Fig.…”

“…We first discuss the data before PA. decreases with increasing C Sb for T g ¼ 375 C. Generally, in poly-Ge, n is determined by the balance between activated n-type dopants and defect-induced acceptors. 18 The lower T g provides the lower solubility limit of Sb in Ge and then the more segregation of excess Sb, which produces defects in Ge. Therefore, the decrease in n with increasing C Sb is likely because of the increase in defect-induced acceptors.…”

High-electron-mobility (370 cm2/Vs) polycrystalline Ge on an insulator formed by As-doped solid-phase crystallization

“…Polycrystalline Ge (poly-Ge) thin films have been formed on insulators at low temperatures using solid-phase crystallization (SPC) 16–20 , laser annealing 21–24 , chemical vapor deposition 25,26 , lamp annealing 27,28 , seed layer technique 29 and metal-induced crystallization (MIC) 30–34 . The poly-Ge layers are naturally highly p-type because of their defect-induced acceptors 35 .…”