In_xGa_1–xP Nanowire Growth Dynamics Strongly Affected by Doping Using Diethylzinc

Abstract

Semiconductor nanowires are versatile building blocks for optoelectronic devices, in part because nanowires offer an increased freedom in material design due to relaxed constraints on lattice matching during the epitaxial growth. This enables the growth of ternary alloy nanowires in which the bandgap is tunable over a large energy range, desirable for optoelectronic devices. However, little is known about the effects of doping in the ternary nanowire materials, a prerequisite for applications. Here we present a study of p-doping of InGaP nanowires and show that the growth dynamics are strongly affected when diethylzinc is used as a dopant precursor. Specifically, using in situ optical reflectometry and high-resolution transmission electron microscopy we show that the doping results in a smaller nanowire diameter, a more predominant zincblende crystal structure, a more Ga-rich composition, and an increased axial growth rate. We attribute these effects to changes in seed particle wetting angle and increased TMGa pyrolysis efficiency upon introducing diethylzinc. Lastly, we demonstrate degenerate p-doping levels in InGaP nanowires by the realization of an Esaki tunnel diode. Our findings provide insights into the growth dynamics of ternary alloy nanowires during doping, thus potentially enabling the realization of such nanowires with high compositional homogeneity and controlled doping for high-performance optoelectronics devices.

InP/GaInP nanowire tunnel diodes

“…Looking next at the inverse GaInP:Zn/InP:S configuration ( Fig. 3(b)), the peak current varies NWs [29,37]. As for the n-InP segments in the four configurations, S doping induced predominately wurtzite (WZ) structure, in line with previous investigation on InP NWs [38].…”

“…Samples were grown in a low-pressure (100 mbar) The total NW length was 2 µm with each segment of 1 µm, mimicking the position of the tunnel diode in a proposed tandem solar cell structure. The NW length was continuously monitored and controlled in situ by use of reflectance spectroscopy [29,30]. To improve pattern preservation, a pre-anneal nucleation of InP was implemented at 280 °C for 1 min at TMIn and PH3 molar fractions of χTMIn = 8.9 × 10 -5 , and χPH3= 6.92 × 10 -3 [25].…”

“…3(a)). The NDR region was observed with a relatively large variation of peak voltage between NWs (ranging from 0.3 to 2 V) which we attributed to the series resistance of the Schottky-like contact to the p-type GaInP segment [19,29]. Under reverse bias, the poor contact explains the large breakdown voltage (~-1 V), which should ideally be close to 0 V for Zener tunneling [33].…”

Electrical and optical evaluation ofn-type doping in InxGa(1−x)P nanowires

“…Before growth of the first contact segment, the growth was initiated with an approximately 0.15 µm long InP stub with trimethylindium (TMIn), and phosphine (PH3), at molar fractions of χTMIn= 8.9 × 10 -5 , χPH3 = 6.9 × 10 -3 ( Fig. 1a) [14]. Thereafter, both contact segments and the middle segment were grown using the precursors of TMIn, trimethylgallium (TMGa) and PH3, at molar fractions of χTMIn= 2.7 × 10 -5 , χTMGa= 1.36 × 10 -3 , and χPH3= 5.4 × 10 -3 .…”

Fundamentals of the nanowire solar cell: Optimization of the open circuit voltage

“…a planar Si cell. The principle of a nanowire tandem cell has been first demonstrated by Heurlin et al 198 200 , while a radial tunnel junctions has recently been demonstrated by Tizno et al 201 . Although a multi-junction nanowire solar cell has not yet been realized experimentally, we like to emphasize that semiconductors with different lattice constant can be stacked into a single nanowire.…”