Investigation of Pd/MoOx/n-Si diodes for bipolar transistor and light-emitting device applications

Abstract

Sub-stoichiometric molybdenum oxide (MoO x ) has recently been investigated for application in high efficiency Si solar cells as a "hole selective" contact. In this paper, we investigate the electrical and light-emitting properties of MoO x -based contacts on Si from the viewpoint of realizing functional bipolar devices such as light-emitting diodes (LEDs) and transistors without any impurity doping of the Si surface. We realized diodes on n-type Si substrates using e-beam physical vapor deposition of Pd/MoO x contacts and compared their behavior to implanted p þ n-Si diodes as a reference. In contrast to majority-carrier dominated conduction that occurs in conventional Schottky diodes, Pd/MoO x /n-Si diodes show minority-carrier dominated charge transport with I-V, C-V, and light-emitting characteristics comparable to implanted counterparts. Utilizing such MoO x -based contacts, we also demonstrate a lateral bipolar transistor concept without employing any doped junctions. A detailed C-V analysis confirmed the excessive band-bending in Si corresponding to a high potential barrier (.0:90 V) at the MoO x /n-Si interface which, along with the observed amorphous SiO x (Mo) interlayer, plays a role in suppressing the majority-carrier current. An inversion layer at the n-Si surface was also identified comprising a sheet carrier density greater than 8:6 Â 10 11 cm À2 , and the MoO x layer was found to be conductive though with a very high resistivity in the 10 4 Ω-cm range. We refer to these diodes as metal/non-insulator/semiconductor diodes and show with our device simulations that they can be mimicked as high-barrier Schottky diodes with an induced inversion layer at the interface.

Inversion Charge Study in TMO Hole-Selective Contact-Based Solar Cells

“…For negative bias we observe a linear dependence of 1/C 2 with the applied voltage for frequencies from 20 kHz to 500 kHz. This behavior was previously observed by Gupta et a [25]. for Pd/MoO x /n-Si junctions in the 10 khz-…”

“…The proposed band diagram of this type of solar cells is very similar to a Schottky junction [20]. Some authors, like Gupta et al studied this approach in Pd/MoOx/n.Si diodes [25]. In a previous work, we measured the currentvoltage characteristics at different temperatures for a MoO x based solar cell obtaining similar results.…”

Low temperature pure boron layer deposition for Si diode and micromachining applications

“…This means that at a certain forward bias voltage, the hole current will saturate and no longer increase exponentially with the voltage. This effect may be difficult to identify in the measurements because the high current also means that the series resistance has a large impact and can attenuate the current already at low forward voltages [110,111]. In Fig.…”

Nanometer-thin pure boron CVD layers as material barrier to Au or Cu metallization of Si

“…However, in reality, chemical reactions at the metal-silicon interface will often modify the experimentally observed SBH [23]. Much work has been devoted to developing layers between the metal and Si to disrupt this effect and nevertheless get either a low SBH, mainly for the purpose of making more low ohmic contacts [24], or, oppositely, a high SBH for increasing hole injection and/or reducing electron injection [25]. In this paper, it was also demonstrated that in simulations of experimental results, the effect of the interface and surrounding (charged) layers can often be reproduced by assuming the diode to have an appropriate SBH and surface recombination velocity.…”