Improved Vertical Carrier Transport for Green III-Nitride LEDs Using (In,Ga)N Alloy Quantum Barriers

Abstract

We report on experimental and simulation-based results using (In, Ga)N alloy quantum barriers in c-plane green light-emitting diode (LED) structures as a means to improve vertical carrier transport and reduce forward voltage (V F ). Three-dimensional device simulations that include random alloy fluctuations are used to understand carrier behavior in a disordered potential. The simulated current density-voltage (J -V) characteristics and modified electron-hole overlap |F mod | 2 indicate that increasing the indium fraction in the (In, Ga)N quantum barriers leads to a reduced polarization discontinuity at the interface between the quantum barrier and quantum well, thereby reducing V F and improving |F mod | 2 . Maps of electron and hole current through the device show a relatively homogenous distribution in the XY plane for structures using GaN quantum barriers; in contrast, preferential pathways for vertical transport are identified in structures with (In, Ga)N barriers as regions of high and low current. A positive correlation between hole (electron) current in the p-side (n-side) barrier and indium fraction reveals that preferential pathways exist in regions of high indium content. Furthermore, a negative correlation between the strain ε zz and indium fraction shows that high indium content regions have reduced strain-induced piezoelectric polarization in the Z direction due to the mechanical constraint of the surrounding lower indium content regions. Experimentally, multiple quantum well green LEDs with (In, Ga)N quantum barriers exhibit lower V F and blue-shifted wavelengths relative to LEDs with GaN quantum barriers, consistent with simulation data. These results can be used to inform heterostructure design of low V F , long-wavelength LEDs and provide important insight into the nature of carrier transport in III-nitride alloy materials.

Impact of random alloy fluctuations on the carrier distribution in multicolor ( In , Ga ) NO’Donovan, Farrell, Moatti et al. 2024Phys. Rev. Applied0000View full textAdd to dashboardCite

“…Furthermore, B 0 , C p and C n will also be carrier density dependent [18,52,53]. We follow here the widely made assumption that these coefficients are constant across the InGaN MQW region [23,25]. In the following we take a weighted average of parameters calculated in Ref.…”

“…Experimental and theoretical studies on the electronic [15][16][17] and optical [18,19] properties of (In,Ga)N systems have already revealed that these properties are significantly impacted by alloy fluctuation induced carrier localization effects. However, the impact of alloy disorder on the carrier transport has only been targeted recently [20][21][22][23][24][25]. Here, studies are ranging from fully atomistic quantum mechanical approaches [20] up to modified continuum-based models [21][22][23][24][25].…”

“…However, the impact of alloy disorder on the carrier transport has only been targeted recently [20][21][22][23][24][25]. Here, studies are ranging from fully atomistic quantum mechanical approaches [20] up to modified continuum-based models [21][22][23][24][25]. Previously in the literature, transport through a disordered alloy has been addressed with a continuum approach by creating a random distribution of atoms, and averaging over a volume to get a "local" alloy content [23,25].…”

“…Here, studies are ranging from fully atomistic quantum mechanical approaches [20] up to modified continuum-based models [21][22][23][24][25]. Previously in the literature, transport through a disordered alloy has been addressed with a continuum approach by creating a random distribution of atoms, and averaging over a volume to get a "local" alloy content [23,25]. This was then used to determine fluctuating conduction and valence band confining energies.…”

Injection mechanisms in a III -nitride light-emitting diode as seen by self-emissive electron microscopy

“…However, the polarization barriers and band offsets increase for longer wavelength LEDs such that large driving voltages are required for vertical transport. These large driving voltages could result in large junction biases, where a significant proportion of the injected electrons could overflow the QWs directly to the p-side of the diode [13,39].…”