High injection and carrier pile-up in lattice matched InGaAs/InP PN diodes for thermophotovoltaic applications

Abstract

This article analyzes and explains the observed temperature dependence of the forward dark current of lattice matched In0.53Ga0.47As on InP diodes as a function of voltage. The experimental results show, at high temperatures, the characteristic current-voltage (I–V) curve corresponding to leakage, recombination, and diffusion currents, but at low temperatures an additional region is seen at high fields. We show that the onset of this region commences with high injection into the lower-doped base region. The high injection is shown by using simulation software to substantially alter the minority carrier concentration profile in the base, emitter and consequently the quasi-Fermi levels (QFL) at the base/window and the window/cap heterojunctions. We show that this QFL splitting and the associated electron “pile-up” (accumulation) at the window/emitter heterojunction leads to the observed pseudo-n=2 region of the current-voltage curve. We confirm this phenomenon by investigating the I–V–T characteristics of diodes with an InGaAsP quaternary layer (Eg=1 eV) inserted between the InP window (Eg=1.35 eV) and the InGaAs emitter (Eg=0.72 eV) where it serves to reduce the barrier to injected electrons, thereby reducing the “pile-up.” We show, in this case that the high injection occurs at a higher voltage and lower temperature than for the ternary device, thereby confirming the role of the “accumulation” in the change of the I–V characteristics from n=1 to pseudo-n=2 in the ternary latticed matched device. This is an important phenomenon for consideration in thermophotovoltaic applications. We, also show that the activation energy at medium and high voltages corresponds to the InP/InGaAs conduction band offset at the window/emitter heterointerface.

Microscale radiation in thermophotovoltaic devices—A review

“…Whale and Cravalho (2002) demonstrated efficiency as a function of the band gap of In x Ga 1Àx As cells at different alloy compositions in a MTPV device. Ginige et al (2004) analysed the temperature dependence of the forward diode current in In 0.53 Ga 0.47 As cell. Recently, InGaAs TPV cells with band gap of 0.6 eV were used for space applications in radioisotope-fired TPV systems.…”

A Comparative Study of Front and Back Illuminated Strain Balanced InGaAs MQW Thermophotovoltaic Cells on n-InP Substrate For High Power Applications

“…At these high light intensities, the maximum power voltage (see table 2) is in a region not dominated by 'shunting'. Examination of the dark IV characteristics shown in figure 1 indicates that the maximum power voltage is in a region where radiative recombination dominates over non-radiative recombination [6]. From this we conclude that this lower FF of the conventional cell to be due to lateral resistance in the emitter layer.…”

Characterization of bulk and surface currents in strain-balanced InGaAs quantum-well mesa diodes

“…2(a) and 2(b) we compare the dark current density, J -V and n -V of the SB-MQW with the LM diodes. The ideality for the LM diode is seen to be near "ideal," i.e., n = 1, for voltages between 0.25 and 0.5 V. The increase in n, observed at the higher voltages, is due to carrier "pileup" 7 giving rise to a pseudo n = 2 regime. For the SB-MQW different recombination mechanisms dominate at different voltages as the carrier density increases which in turn alters the extracted ideality factor.…”