G. N. Talalakin

Towards efficient mid-IR LED operation: optical pumping, extraction or injection of carriers?

Positive and negative output power, spectral and current—voltage characteristics of the In(Ga)As and InAs(Sb) based heterostructure light-emitting diodes with the ‘episide-down’ construction grown onto heavily doped n+-InAs have been examined in the 20-200°C temperature range. Optically pumped LEDs composed from the above heterostructures or from InSb exhibited output characteristics fairly close to the conventional LEDs. Wavelength and temperature variation of the emission power in the 3.3–8 μm spectral range was compared with the phenomenological model based on the expectations of the negative luminescence power (NLP) and saturation current (I sat). The crossover of forward bias power at 1 A and negative power at I = I sat takes place at 90 and 160°C for 5.3 and 4.3 μm LEDs correspondingly.

Gadolinium-doped InGaAsSb solid solutions on an InAs substrate for light-emitting diodes operating in the spectral interval λ=3–5 µm

The influence of a gadolinium impurity on the electrical and luminescence characteristics of epitaxial structures made from narrow-gap n-InGaAsSb solid solutions grown by liquid-phase epitaxy on InAs substrates is investigated. The addition of gadolinium to the flux solution in the interval of concentrations 0<XGdl⩽0.14 at. % has the effect of lowering the density of electrons in the InGaAsSb layers from (3–6)×1016 cm−3 to (7–8)×1015 cm−3 and increasing the carrier mobility from 32 000 cm2/(V·s) to 61 500 cm2/(V·s) (T=77 K). Also observed are a decrease in the half-width of the photoluminescence spectra from 25 meV to 12 meV and as much as a tenfold increase in their intensity (T=77 K). The electroluminescence intensity of LEDs fabricated from gadolinium-doped n-InGaAsSb/p-InAs epitaxial structures (T=300 K) increases approximately a factor of 2 relative to the undoped samples.

Negative luminescence in p-InAsSbP/n-InAs diodes

Negative luminescence (NL) at λmax=3.8 µm from reverse-biased p-InAsSbP/n-InAs diode heterostructures has been studied at temperatures of 70–180°C. The NL power increases with temperature and exceeds the power of direct-bias electroluminescence at temperatures over 110°C. An NL power of 5 mW/cm2, efficiency of 60%, and a conversion efficiency of 25 mW/(A cm2) have been obtained at 160°C.

Light emitting diodes for the spectral range λ=3.3–4.3 µm fabricated from InGaAs and InAsSbP solid solutions: Electroluminescence in the temperature range of 20–180°C (Part 2)

Light-emitting diodes (LEDs) based on p-n homo-and heterostructures with InAsSb(P) and InGaAs active layers have been designed and studied. An emission power of 0.2 (λ=4.3 µm) to 1.33 mW (λ=3.3 µm) and a conversion efficiency of 30 (InAsSbP, λ=4.3 µm) to 340 mW/(A cm2) (InAsSb/InAsSbP double heterostructure (DH), λ=4.0 µm) have been achieved. The conversion efficiency decreases with increasing current, mainly owing to the Joule heating of the p-n homojunctions. In DH LEDs, the fact that the output power tends to a constant value with increasing current is not associated with active region heating. On raising the temperature from 20 to 180°C, the emission power of the (λ=3.3 and 4.3 µm) LEDs decreases, respectively, 7-and 14-fold, to become 50 (at 1.5 A) and 7 µW (at 3 A) at 180°C.

Optically pumped mid-infrared InGaAs(Sb) LEDs

Spectral and power characteristics of optically pumped light-emitting diodes (LEDs) for the 3.1–3.6 µm range are presented. The LED structure contains narrow-gap InGaAs or InGaAsSb layers on an n+-InAs substrate; the pumping is done with a GaAs LED. A conversion efficiency of 90 mW/(A cm2), comparable with that for injection LEDs, is achieved.

Negative luminescence at 3.9 µm in InGaAsSb-based diodes

Current-voltage characteristics, as well as spectral and power-current characteristics, for the emission of InAsSbP/InGaAsSb double-heterostructure diodes grown on InAs substrates were measured under forward and reverse biases in the temperature range of 25–90°C. It was shown that the conversion efficiency for negative luminescence, which occurs due to the extraction of charge carriers from the regions adjacent to the p-n junction at temperatures ∼90°C, is higher than the conversion efficiency for electroluminescence. Narrowing of the negative luminescence spectra in diodes with a built-in cavity was observed.

Gain and internal losses in InGaAsSb/InAsSbP double-heterostructure lasers

We report on a study characterizing internal losses and the gain in InGaAsSb/InAsSbP diode-heterostructure lasers emitting in the mid-infrared (3–4 µm). Numerical simulations of the current dependence of the intensity of spontaneous emission above the laser threshold and of the differential quantum efficiency allowed us to determine the intraband absorption k0 ≈5.6×10−16 cm2. The cavity-length dependence of the threshold current is used to estimate the internal losses at zero injection current α0≈5 cm−1. Calculations of the internal losses at laser threshold showed that they increase more than fourfold when the cavity length is decreased from 500 µm to 100 µm. The temperature dependence of the differential quantum efficiency is explained on the assumption that intraband absorption with hole transitions into a split-off band occurs. It is shown that the maximum operating temperature of “short-cavity” lasers is determined by the intraband absorption rather than by Auger recombination. The internal losses are shown to have a linear current dependence. The separation of the quasi-Fermi levels as a function of current demonstrates an absence of voltage saturation of the p-n junction above threshold.

Lattice-matched GaInPAsSb/InAs structures for devices of infrared optoelectronics

It is reported that a Ga0.92In0.08P0.05As0.08Sb0.87 quinary solid solution, which is lattice-matched to InAs, with a band gap of 695 meV (77 K) and 640 meV (300 K) is obtained. It is demonstrated that a heterojunction of type II is realized in the InAs/Ga0.92In0.08P0.05As0.08Sb0.87 structure. The solid solution obtained was used for the development of prototypes of light-emitting diodes and photodiodes with the highest intensity of emission and photosensitivity in the vicinity of 1.9 µm.

InGaAsSb(Gd)/InAsSbP double heterostructure lasers (λ=3.0–3.3 µm) for diode laser spectroscopy

Data on threshold currents, the differential quantum efficiency, the emission spectrum, current tuning, and radiation power of mesastripe InGaAsSb(Gd)/InAsSbP double heterostructure lasers with λ=3.0–3.3 µm and a cavity length of 70–150 µm in a temperature range of 50–107 K are reported. In the experiments, the threshold currents Ith<10 mA, a total output power of 0.5 mW/facet, and a single-mode power of 0.43 mW at 77 K in the cw regime were obtained. Lasers operated in the single-mode regime at currents I≤6Ith, the spectral purity was as high as 650: 1, the tuning rate was 210 cm−1/A, and the tuning range was 10 cm−1 wide. An example of methane detection at 3028.75 cm−1 is presented.

Long-wavelength uncooled sources of λ=5–6 μ radiation using graded-index InAsSb(P) layers grown by liquid-phase epitaxy

Graded-index p-n InAsSb/InAsSbP/InAs structures capable of emitting at the maximum of the spectral curve up to 5.4 μm with a half-width of ∼26 meV (∼0.6 μm) without cooling have been fabricated and studied. This is the longest-wavelength radiation obtained at room temperature in III–V structures grown by liquid-phase epitaxy and the band is the narrowest obtained for semiconductor spontaneous radiation sources.