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

We compare the electrical and optical characteristics of mesa diodes based on In0.62Ga0.38As/In0.45Ga0.55As strain-balanced multiple-quantum wells (SB-MQW) with lattice-matched (LM) In0.53Ga0.47As diodes. The dark current density of the SB-MQW devices is at least an order of magnitude lower than the LM devices for voltages >0.4 V. Sidewall recombination current is only measured on SB-MQW diodes when exposed to a damaging plasma. While radiative recombination current dominates in the SB-MQW diodes, it is less than the diffusive current in the LM diodes for the same applied voltage. (C) 2004 American Institute of Physics. (DOI:10.1063/1.1835537

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

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 (E-g=1 eV) inserted between the InP window (E-g=1.35 eV) and the InGaAs emitter (E-g=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

InP-based lattice-matched InGaAsP and strain-compensated InGaAs∕InGaAs quantum well cells for thermophotovoltaic applications

Quantum well cells (QWCs) for thermophotovoltaic (TPV) applications are demonstrated in the InGaAsP material system lattice matched to the InP substrate and strain-compensated InGaAs/InGaAs QWCs also on InP substrates. We show that lattice-matched InGaAsP QWCs are very well suited for TPV applications such as with erbia selective emitters. QWCs with the same effective band gap as a bulk control cell show a better voltage performance in both wide and erbialike emission. We demonstrate a QWC with enhanced efficiency in a narrow-band spectrum compared to a bulk heterostructure control cell with the same absorption edge. A major advantage of QWCs is that the band gap can be engineered by changing the well thickness and varying the composition to the illuminating spectrum. This is relatively straightforward in the lattice-matched InGaAsP system. This approach can be extended to longer wavelengths by using strain-compensation techniques, achieving band gaps as low as 0.62 eV that cannot be achieved with lattice-matched bulk material. We show that strain-compensated QWCs have voltage performances that are at least as good as, if not better than, expected from bulk control cells