Electrical characterization of n-type a-SiGe:H/p-type crystalline-silicon heterojunctions

Abstract

Heterojunctions with an n-type hydrogenated amorphous silicon germanium (a-SiGe:H) on p-type crystalline-silicon heterojunctions were fabricated and electrically characterized. The electrical characterization was made by current density-voltage (J -V ) and capacitance-voltage (C-V ) measurements. The C-V results confirm the existence of an abrupt heterojunction. The temperature dependence of the J -V curves shows that in the forward conduction at low bias voltage (V < 0.45 V) the current density is determined by the recombination on the n-type a-SiGe:H depletion region, while at higher voltages (V > 0.5 V), the space charge limited effect becomes the main transport mechanism. The conduction and valence band discontinuities of the heterojunction and the electron affinity of the n-type a-SiGe:H film were calculated using Anderson's model. Under reverse bias conditions the J -V curves suggest that the current density is limited by hopping through the localized states into the gap. One-dimensional (1D) simulations support the proposed transport mechanisms.

Analytical Drain Current Model for a-SiGe:H Thin Film Transistors Considering Density of States

“…Furthermore, defects parameters that define the density of states of a-SiGe:H layer used for simulations and modeling are shown in Table 2. Some of those values were taken from [20]. Figure 3 shows the comparison of modeled (lines) and simulated (symbols) characteristics I DS vs V DS for V GS = 1, 2, 3 and 4 Volts.…”

“…Tail bands consist of a donor-like valence band, g TA (E), and an acceptor-like conduction band, g TD (E). On the other hand, deep bands are composed of a donor-like valence band, g GA (E), and an acceptor-like conduction band, g GD (E), which are represented as follow, [20]:…”

Band offsets and transport mechanisms of hydrogenated nanocrystalline silicon/crystalline silicon heterojunction diode: Key properties for device applications

“…The band discontinuity of the semiconductor heterostructure has been recognized as the fundamental problem of HJ devices, and a number of electrical and optical techniques have been developed to determine the band offset parameters, in which C-V analysis has been widely 18 used in various silicon based anisotype HJs, such as a-Si:H/c-Si, 19 SiGe/ c-Si, 20 and a-SiGe: H / c-Si. 21 In order to obtain correct results from the C-V data, prerequisite material parameters of nc-Si:H should be accurately provided first of all. Compared with its well-known crystalline counterpart, the hydrogenated nanocrystalline Si exhibits quite different physical properties, especially in the band gap, the static dielectric constant, and the effective mass of the electron, which are critical values in yielding reliable band structure for nc-Si: H / c-Si HJ ͓as schematically shown in Fig.…”

Development of Low-Temperature Ambipolar a-SiGe:H Thin-Film Transistors Technology

“…This film is barely used as active layer for TFTs, since a high content of germanium increases the density of states (DOS) in the films. However, a low incorporation of germanium improves some properties of the amorphous films [28][29][30].…”