Interface Properties of GaP/Si Heterojunction Fabricated by PE‐ALD

Abstract

The properties of n‐GaP/p‐Si interface as well as their influence on solar cell performance are studied for GaP layers grown by low‐temperature (380 °C) plasma‐enhanced atomic layer deposition (PE‐ALD). The influence of different plasma treatments and RF power values are explored. The increase of RF power leads to a growth transition from amorphous (a‐GaP) to microcrystalline GaP (μc‐GaP) with either amorphous‐GaP/Si or epitaxial‐GaP/Si interface, respectively. However, when continuous hydrogen plasma is used the amorphous‐GaP/Si interface exhibits better photovoltaic performance compared to the epitaxial one. Values of open circuit voltage, Voc = 0.45–0.55 V and internal quantum efficiencies, IQE > 0.9 are obtained for amorphous‐GaP/Si interfaces compared to Voc = 0.25–0.35 V and IQE < 0.45 for epitaxial‐GaP/Si interfaces. According to admittance spectroscopy and TEM studies the near‐surface (30–50 nm) area of the Si substrate is damaged during growth with high RF power of hydrogen plasma. A hole trap at the level of EV + (0.33 ± 0.02) eV is detected by admittance spectroscopy in this damaged Si area. The damage of Si is not observed by TEM when the deposition of the structures with epitaxial‐GaP/Si interface is realized by a modified process without hydrogen plasma indicating that the damage of the near‐surface area of Si is related to hydrogen plasma interaction.

Study of GaP Nucleation Layers Grown on Si by Plasma‐Enhanced Atomic Layer Deposition

“…A negative effect of the high RF power hydrogen plasma used in this process was reported in Gudovskikh et al and Geissbuhler et al, where the damage in the Si subsurface region was observed by TEM. Moreover, a defect‐rich area was detected in Si within 30–50 nm of the GaP/Si interface by admittance spectroscopy . On the contrary, the low lateral conductivity of the GaP/Si heterojunction fabricated with hydrogen plasma did not allow us to perform Hall effect measurements in the previous study.…”

“…Damaged regions in Si near the interface could be observed in the samples prepared under continuous hydrogen plasma. However, the most important is the fact that the first 3–5 nm of GaP was grown epitaxially on the Si surface for both processes as was previously reported …”

“…One of the direct ways to detect defects in semiconductors is space charge capacitance measurements. In particular, admittance spectroscopy ( C – T – f and G – T – f measurements) was already successfully applied to detect defects in GaP/Si heterojunctions . The Fermi level ( E F ) in the space charge region of the junction should cross the trap level ( E t ) to observe a response in the admittance spectra.…”

“…Here we propose to grow a GaP nucleation layer by low‐temperature (380 °C) plasma‐enhanced atomic layer deposition (PE‐ALD). Previously, the conformal 2D epitaxial growth of a few nanometers of GaP on an Si surface by PE‐ALD was demonstrated . This is an essential basis to explore the capability of this technique to prepare GaP/Si templates for subsequent epitaxial growth of III–V compounds.…”

Advances in Silicon‐Nanoelectronics, Nanostructures and High‐Efficiency Si‐Photovoltaics

“…The integration of silicon with III‐V semiconductors via ALD‐grown nucleation layers is investigated in ref. , while ref. is about quantum cutting, and ref.…”