n-PbSe/p-GaAs LEDs: Hybrid Mid-IR Heterojunction

• n-PbSe/p-GaAs LEDs are mid-infrared hybrid heterojunction devices using p-GaAs as a substrate/contact and thin PbSe as the active emitter.
• The device exploits PbSe’s low Auger-Meitner recombination and GaAs's mature platform to achieve 3.8 µm emission with up to 400 µW output power.
• Epitaxial engineering with high-temperature nucleation and rapid annealing manages an 8% lattice mismatch and high defect density for practical device performance.

n-PbSe/p-GaAs LEDs are mid-infrared hybrid IV-VI/III-V heterojunction light-emitting diodes in which p-GaAs functions as the bottom contact and substrate, a thin PbSe region provides the active emitter, and Sb-doped n-PbSe forms the top emitting/contact layer. In the reported implementation, the device is an electrically injected n-PbSe/p-GaAs heterojunction LED that emits at 3.8 µm, reaches output powers up to 400 µW under pulsed operation, and exhibits a peak wall-plug efficiency of 0.08% at room temperature, despite a lattice mismatch to GaAs of about 8% and threading dislocation densities on the order of $10^9\ \text{cm}^{-2}$ (Meyer et al., 13 Aug 2025). Broader PbSe LED literature provides relevant background on PbSe emissive properties, photoluminescence quantum yield enhancement, surface passivation, and general LED efficiency concepts, but it does not directly analyze the PbSe/GaAs junction or provide device-specific metrics for n-PbSe/p-GaAs LEDs (Liu et al., 2019).

1. Device identity and heterostructure

The reported n-PbSe/p-GaAs LED is described as a hybrid p-i-n-style heterojunction LED in which the GaAs substrate is not just a growth template, but part of the electrical junction. The device uses p-GaAs as the bottom contact/substrate, a thin PbSe active region, and Sb-doped n-PbSe as the top emitting/contact layer. The specific PbSe LED stack consists of a 25 nm PbSe nucleation layer grown at elevated temperature to establish (001) cube-on-cube epitaxy, followed by 450 nm unintentionally doped PbSe and 100 nm Sb-doped n-PbSe, thereby creating the electrically injected n-PbSe/p-GaAs heterojunction (Meyer et al., 13 Aug 2025).

This architecture is distinct from colloidal quantum-dot LED implementations. The device is an epitaxial hybrid heterojunction that uses GaAs simultaneously as a mechanically robust platform and as an active electrical partner in the junction. A plausible implication is that the structure should be understood less as PbSe deposited on an inert host and more as a compound heterojunction in which both material families contribute to device operation.

2. Materials complementarity and mid-infrared rationale

The materials rationale is based on complementarity between IV-VI PbSe and III-V GaAs. PbSe belongs to the IV-VI rocksalt semiconductor family, which is described as having intrinsically low Auger-Meitner recombination compared with typical narrow-gap III-V or II-VI semiconductors. This is important because strong nonradiative Auger-Meitner recombination is identified as the primary limitation on the room-temperature efficiency of III-V-based mid-IR LEDs. GaAs, by contrast, is used because it offers excellent mechanical stability, high thermal conductivity relative to native IV-VI substrates, a mature III-V processing ecosystem, and the ability to serve as a junction partner in a hybrid heterostructure (Meyer et al., 13 Aug 2025).

The resulting design objective is not merely material integration for its own sake. It is explicitly aimed at exploiting the intrinsically low Auger-Meitner recombination rates of PbSe while leveraging the mature III-V platform. The same study extends the concept by incorporating 7% Sn in PbSnSe, which shifts emission to 5 µm in GeSe/PbSnSe/GaAs LEDs, indicating that alloying within the IV-VI subsystem provides a route to longer-wavelength hybrid emitters (Meyer et al., 13 Aug 2025).

3. Epitaxy under large mismatch

A defining feature of the n-PbSe/p-GaAs system is the large lattice mismatch, quantified as about 8%. The mismatch is expressed as

$$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$

The reported strategy is not to eliminate this mismatch, but to manage it through epitaxial engineering. The process uses a high-temperature PbSe exposure on GaAs to promote single-orientation nucleation, followed by lower-temperature growth of the bulk IV-VI layers. Because the thermal expansion coefficient mismatch is also large, about 13 ppm/K, most of the film is grown at approximately $190\,^\circ\mathrm{C}$, and thicker films are enabled by a $375\,^\circ\mathrm{C}$, 300 s rapid thermal anneal under SiO$_2$ capping. The anneal is reported to improve crystallinity and to help allow films thicker than 400 nm without severe cracking (Meyer et al., 13 Aug 2025).

This directly addresses a common misconception that useful optoelectronic heterojunctions necessarily require close lattice matching. In this case, useful operation is achieved by low-temperature epitaxy, nucleation control, and post-growth anneal/capping, rather than by perfect structural registry. This suggests that the hybrid IV-VI/III-V design space is broader than conventional lattice-matched III-V LED design would imply.

4. Band alignment, carrier injection, and recombination

The PbSe/GaAs interface is argued to be likely type-I aligned. In the reported interpretation, this is beneficial because it helps confine both electrons and holes in the PbSe active region. The importance of that point is made explicit: with a thin active layer, type-II or type-III alignment could separate electrons and holes too strongly and would reduce radiative recombination and quench luminescence (Meyer et al., 13 Aug 2025).

The electrical characteristics are analyzed using the standard diode relation

$I = I_0 \left( e^{qV/nkT} - 1 \right),$

with an extracted ideality factor of $n = 1.66$. That value is stated to be consistent with significant trap-assisted recombination in the space-charge region. The electroluminescence efficiency behavior is discussed qualitatively in two regimes: a low-current regime limited by Shockley-Read-Hall recombination and a high-current roll-off attributed to Auger-Meitner recombination and heating. Together, these observations locate the main loss channels in trap-assisted recombination at low injection and combined nonradiative and thermal effects at high injection (Meyer et al., 13 Aug 2025).

5. Defects, defect tolerance, and measured device performance

The hybrid LEDs operate despite threading dislocation densities on the order of $10^9\ \text{cm}^{-2}$. The dislocation density is estimated from XRD rocking curves using

$\rho = \frac{4.35\,\beta^2}{b^2},$

where $\rho$ is the threading dislocation density, $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$0 is the skew-symmetric rocking-curve FWHM, and $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$1 is the Burgers vector magnitude. For the PbSe LED, the threading dislocation density decreases after annealing from $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$2 to $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$3. The reported interpretation is that nonradiative recombination in these IV-VI materials is dominated more by point defects and SRH centers than by dislocations, and that PbSe exhibits defect tolerance associated with its bonding and high dielectric constant. The authors further note that a PbSnSe sample with higher threading dislocation density showed photoluminescence that was only about $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$4 dimmer, not catastrophically worse (Meyer et al., 13 Aug 2025).

The principal room-temperature device metrics are summarized below.

Quantity	Reported value	Conditions or note
PL peak	3.8 µm	room temperature
EL peak	4.0 to 3.7 µm	shifts as current increases
Output power	up to 400 µW	pulsed, 0.8 A injection
L-I characterization	1 kHz, 1% duty cycle	pulsed operation
EL spectra	5 kHz, 50% duty cycle	pulsed operation
Peak wall-plug efficiency	0.08%	room temperature
Ideality factor	$$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$5	diode fit

The wall-plug efficiency is defined as

$$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$6

where $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$7 is the output optical power, $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$8 is the drive current, and $$f = \frac{a_{\text{film}} - a_{\text{sub}}}{a_{\text{sub}}}.$$9 is the forward voltage. The electroluminescence peak shifts slightly to shorter wavelength with increasing current, which is described as likely due to device heating and the unusual temperature dependence of the PbSe bandgap (Meyer et al., 13 Aug 2025).

6. Position within PbSe LED research

The broader PbSe literature most directly relevant to n-PbSe/p-GaAs LEDs comes from work on near-infrared PbSe quantum dots and PbX NIR-QLEDs rather than from prior PbSe/GaAs heterojunction studies. That literature identifies PbSe as a promising emitter because bulk PbSe has a room-temperature bandgap of 0.278 eV, PbSe quantum dots exhibit large excitonic Bohr radii and strong quantum confinement effects, and size control enables emission tuning across a wide spectral range, including the 1200–1400 nm range for high-quality PbSe quantum dots. Reported synthesis routes include canonical hot injection with lead oleate and selenium precursors such as TOP-Se, alongside alternative selenium precursors including TMS-Se, SeO$190\,^\circ\mathrm{C}$0, selenourea, TDP-Se, and OLA-Se. Reported photoluminescence quantum yield improvements range from reproduced PbSe quantum dots with 12% to 81% PLQY, to 85% through improved lead precursor selection, and up to 100% with 1,2-hexadecanediol-assisted synthesis. Surface engineering strategies include PbSe/CdSe core/shell structures and halide treatments using Cl$190\,^\circ\mathrm{C}$1, Br$190\,^\circ\mathrm{C}$2, and I$190\,^\circ\mathrm{C}$3, with air stability reported for as long as 24 months. For PbX NIR-QLEDs, the review emphasizes that $190\,^\circ\mathrm{C}$4 and $190\,^\circ\mathrm{C}$5 are especially critical to external quantum efficiency, and it cites a progression from 0.5% EQE in 2000 to 7.9% EQE at 1400 nm in 2018 for PbX-based devices, although the highest-performing examples summarized there are mostly PbS-based rather than PbSe/GaAs devices (Liu et al., 2019).

Equally important is what that literature does not provide for the present topic. The PbX review contains no direct experimental discussion of n-type PbSe on p-type GaAs, no PbSe/GaAs band diagram, no discussion of electron or hole injection at a PbSe/GaAs interface, no specific recombination mechanism in a PbSe/GaAs junction, and no turn-on voltage, current efficiency, power efficiency, stability data, or fabrication sequence for epitaxial PbSe on GaAs. The consequence is that n-PbSe/p-GaAs LEDs should be situated primarily within the hybrid IV-VI/III-V heterojunction literature, while the PbSe quantum-dot literature serves as indirect background on emitter quality, passivation, and efficiency concepts rather than as direct precedent for the PbSe/GaAs junction itself (Liu et al., 2019).

7. Benchmarking and significance

The reported n-PbSe/p-GaAs LED is compared directly with commercial III-V mid-IR LEDs. Commercial devices at similar wavelengths are cited as falling in the 0.1–1% wall-plug-efficiency range, and the reported 0.08% WPE of the PbSe/GaAs device is described as close to the low end of that range, while still below the best commercial III-V LEDs. The study further states that the device output power and WPE are already on par with some commercial LEDs at similar wavelengths (Meyer et al., 13 Aug 2025).

The broader significance assigned to the hybrid architecture is that it avoids heavily engineered quantum cascade or interband cascade structures and the complex active-region designs typically required to suppress Auger losses in III-V mid-IR emitters. Instead, it combines PbSe for low-Auger mid-IR emission with GaAs for a mature substrate and electrical platform. This suggests a distinct design philosophy for mid-IR emitters: rather than compensating for unfavorable recombination physics through increasingly elaborate III-V active regions, the hybrid IV-VI/III-V approach begins from a material system with intrinsically favorable Auger-Meitner behavior and then integrates it onto a technologically mature III-V foundation (Meyer et al., 13 Aug 2025).