A single InGaN/GaN multiple quantum wells microwire light-emitting diode with high efficiency current injection and spreading

Injection current, and temperature, dependences of the electroluminescence (EL) spectrum from green InGaN/GaN multiple quantum well (MQW)-based light-emitting diodes (LED) grown on a Si substrate, are investigated over a wide range of injection currents (0.5 µA-350 mA) and temperatures (6-350 K). The results show that an increasing temperature can result in the change of injection current-dependent behavior of the EL spectrum in initial current range. That is, with increasing the injection current in the low current range, the emission process of the MQWs is dominated by filling effect of low-energetic localized states at the low temperature range of around 6 K, and by Coulomb screening of the quantum confinement Stark effect followed by a filling effect of the higher levels of the low-energetic localized states at the intermediate temperature range of around 160 K. However, when the temperature is further raised to the higher temperature range of around 350 K, the emission process of the MQWs in the low current range is dominated by carrier-scattering effect followed by non-radiative recombination process. The aforementioned current-dependent behaviors of the EL spectrum are mainly attributed to the strong localized effect of the green LED, as confirmed by the anomalous temperature dependence of the EL spectrum measured at the low injection current of 5 µA. In addition, the injection current dependence of external quantum efficiency at different temperatures shows that, with increasing temperature from 6 to 350 K, in addition to the enhanced non-radiative recombination, electron overflow becomes more significant, especially in the higher temperature range above 300 K.

Structural and optical characteristics of InN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

We study hole transport behavior of InGaN/GaN light-emitting diodes with the dual wavelength emission method. It is found that at low injection levels, light emission is mainly from quantum wells near p-GaN, indicating that hole transport depth is limited in the active region. Emission from deeper wells only occurs under high current injection. However, with Mg-doped quantum barriers, holes penetrate deeper within the active region even under low injection, increasing the radiative recombination. Moreover, the improved hole transport leads to reduced forward voltage and enhanced light generation. This is also verified by numerical analysis of hole distribution and energy band structure.

We studied and improved gallium nitride (GaN) nanowire (NW) based light emitting diodes (LEDs). PIN nanodiodes with and without InGaN/GaN multiple quantum wells (MQWs) were grown by molecular beam epitaxy (MBE) under N‐rich conditions on n‐doped Si(111) substrates. Thanks to the coalescence of the p‐type region of the NWs grown at low temperature, an autoplanarization process has been performed to obtain LEDs. Ni/Au top contacts have been deposited and patterned in order to bias the devices. A multiple‐scale characterization approach has been carried out through the comparison of localized cathodoluminescence (CL) and macroscopic electroluminescence (EL) spectra. It shows that the EL emission of PIN‐based LED at room temperature is related to defects in the p‐type region of the NWs. In order to enhance the radiative recombinations of NW‐based LEDs, we have first added InGaN/GaN MQWs, and secondly an electron blocking layer (EBL) has been inserted between the MQWs and the p‐type zone of the NWs. The LED with EBL exhibited an emission band at 420 nm. The blue‐shift of this emission band with increasing injected current is attributed to quantum confined Stark effect (QCSE) and evidences the radiative emission of InGaN/GaN MQWs. At 50 mA dc current, this improved NW‐based LED emits about 500 times more light than the heterostructure without EBL.

A novel method for the characterization of multiple quantum well(MQW) light emitting diodes(LEDs) is investigated. This method involves the measurement of photocurrent generation in an LED when irradiated with photons of energy near the absorption edge of the quantum wells. In this situation the I-V curve of the LED reveals a number of photocurrent oscillation zones corresponding to spatial variations in the heterostructure (Figure 1). The mechanism leading to the voltage-bias dependence of these features is hypothesized to be the expansion of the depletion (space-charge) region. Electrons and holes, from the N and P regions respectively, are drawn to the P-N junction as the reverse bias-voltage is increased. The area occupied by the ionized dopant atoms left behind by these charges is referred to as the ‘depletion region’. As the magnitude of the bias increases this area of depleted atoms becomes larger, engulfing the quantum wells in series. An electric field forms between the charges gathered at the P-N junction and the ionized atoms, giving rise to a potential gradient across the depletion region. The I-V features are then caused by the dynamics of the excited electrons as the potential gradient traverses each quantum well. A preliminary model is constructed by using the SIMS data (Figure 2) for the LED heterostructure supplied by Veeco. The spatial extent of the depleted region is calculated as a function of the applied bias using a doping profile derived from the SIMS data. This allows the estimation of the voltage at which each quantum well will become depleted and thus when a feature will be expected. The resulting curve is compared to the experimentally determined I-V feature spacing. The wavelength and temperature dependencies of this phenomenon are discussed, citing examples from existing literature. The benefits of this method of analysis are examined in terms of acquisition speed, measurement resolution and hardware cost with respect to current techniques such as capacitance-voltage measurement. Further research into this effect would involve the spectral transmission of the MQW devices as a function of voltage bias and the possible applications in spectrometry or optical filtering. A more complete picture of the quantum mechanical interaction between the incident photons, quantum wells, and potential gradient would also be valuable for the interpretation of the I-V curves and possible engineering applications.

InGaN/GaN light-emitting diodes (LEDs) with graded-composition multiple quantum wells (GQWs) were designed and theoretically investigated. In the GQW LED structure, the indium composition in In x Ga1−x N QW was decreased sequentially in increments, $$\Delta x$$ , along the [0001] orientation. Across the composition range, the GQW LEDs have high carrier injection efficiencies and enhanced uniform carrier distributions in the multiple quantum wells because of the band structure. When $$\Delta x = 0.01$$ , the light output power the GQW LED was enhanced by 4.2 % compared with that of the original LED, which corresponds to an increase of IQE of 4.5 % at 180 mA. However, when $$\Delta x$$ increased to 0.02, the light output power of the GQW LEDs was reduced by 3.1 % compared with that of original LED, which corresponds to a decrease of IQE of 3.3 % at 180 mA. Results from the simulations indicated that the device performance was not only related to the carrier injection efficiency and the carrier distribution, but was also related to the balance of electrons and holes in the QWs.

In this paper, we investigate the efficiency enhancement of blue InGaN/GaN light-emitting diodes (LEDs) by incorporating a burried air void photonic crystal (BAVPC) layer within the epitaxial structure. As compared with the conventional patterned sapphire substrate (C-PSS) LEDs and flat sapphire substrate LEDs with BAVPC, the fabricated patterned sapphire substrate (PSS) LEDs with BAVPC exhibit the lowest full-width at half-maximum of (002) and (102) diffraction peaks, the highest light output power of 20.6 mW, and the highest external quantum efficiency of 37.4%. Remarkable performance improvement in the PSS LED with BAVPC is attributed to the better epitaxial quality with threading dislocations terminated by the BAVPC and the higher scattering at interface between GaN and air-void. By positioning the BAVPC directly below the multiple quantum wells (MQWs), it would cause the reduction in the number of trapped optical modes. The methodology optically isolates the MQWs from the underlying substrate and increases the optical output power. Moreover, threading dislocations are significantly suppressed using the BAVPC with high air filling fraction of ~ 50%. It is well proposed that this methodology provides a promising alternative to C-PSS LEDs.

We demonstrate light emission at 280 nm from UV light-emitting diodes consisting of AlInGaN/AlInGaN multiple quantum wells. Turn-on voltage of the devices is ∼5 V with a differential resistance of ∼40 Ω. The peak emission wavelength redshifts ∼1 nm at high injection currents.

In recent years, there has been great research interest in the development of efficient Group III-Nitride Light Emitting Diodes (LEDs) due to the range of wavelengths covered by this material family. Quantum wells play a significant role in the performance of these optoelectronic devices as they enable tuning in emission wavelength and color of light through variation in composition and width of the well.;The time and cost associated with iterative development and optimization of such new semiconductor devices through physical materials growth and device fabrication can be prohibitive to full exploration of potential design spaces. Technology Computer Aided Design (TCAD) simulation tools have emerged allowing engineers to explore design alternatives at an early stage. However simulations, especially for new materials and devices exhibiting quantum effects, must reliably model material and device physics and produce results that correspond to those that would have been achieved experimentally. In this thesis, tiberCAD, Crosslight APSYS and Synopsys tools have been evaluated and used to design and analyze components of, as well as complete Multiple Quantum Well LEDs. The effect of variations of mole fraction, well width, and bias on Energy Levels and Electroluminescence (EL) has been examined. Simulation results have been compared with theory and measurements from grown and fabricated GaN/InGaN Multiple Quantum Well LEDs.

We report on a green light-emitting device, in which the light of an efficient blue 1 mm2 GaInN/GaN light-emitting diode (LED) is converted into green light by an optically pumped GaInN/GaN multiple quantum well structure. This solution reached an efficacy of 127 lm/W, i.e., higher than that of state-of-the-art 1 mm2 GaInN/GaN LEDs emitting directly at the target wavelength, at 350 mA current and 535 nm peak wavelength. Optically pumped converters overcome the design limitations of typical multiple quantum well LEDs, where carrier transport issues limit the maximum number of functioning wells and might help to solve the problem of the green gap.

Internal quantum efficiency improvement of InGaN/GaN multiple quantum well green light-emitting diodes

Luminescence of an InGaN/GaN multiple quantum well light-emitting diode

The temperature dependence of photoluminescence measurement was performed on an undoped In0.126Ga0.874N/GaN multiple quantum well (MQW) structure and a light emitting diode (LED) structure using this MQW as an active region. The emission energy of the LED structure showed a red shift of about 230 meV at room temperature compared with the undoped In0.126Ga0.874N/GaN MQW. This behavior of the LED structure is attributed to the quantum-confined Stark effect due to its p-n junction induced electric field. This conclusion was confirmed by a calculation and a detailed discussion based on the theory of the quantum-confined Stark effect.

InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) with Ni/ITO (5/50 nm) and Pt/ITO (0.8/50 nm) current spreading layer were investigated. The electrical and optical properties of Ni/ITO and Pt/ITO films were also investigated. It was found that the normalized transmittance of Ni/ITO and Pt/ITO films could reach 79.22 and 78.98% at 460 nm, which was almost equal. It was also found that Pt/ITO had showed better linear current–voltage characteristics compared to Ni/ITO contacts. The specific contact resistance for Pt/ITO contacts was 5.88 × 10−2 Ω cm2, while for Ni/ITO contacts, it was 5.66 × 10−1 Ω cm2 i.e. ~10 time more. The EL intensity of blue LED was much higher with Pt/ITO p-contact compared to Ni/ITO p-contact. The forward voltages (VF) of LEDs for two contacts (Ni/ITO and Pt/ITO p-contacts) at 20 mA current injection were found 4.49 and 3.5 V, respectively.

Solid‐state infrared sources designed to emit wavelengths above 2 µm often face challenges in achieving high emission efficiency, minimizing power consumption, and reducing fabrication costs. In response, a 2.4 µm wavelength light emitting diode (LED) is developed using metamorphic In0.83Ga0.17As/InAs0.3P0.65Sb0.05 multiple quantum well (MQW) heterostructures. The substantial conduction (94 meV) and valence band offsets (300 meV) within this type‐I MQW LED architecture result in strong carrier confinement, improving electron and hole wavefunction overlap. Despite a notable lattice mismatch of 2.0% between the MQWs and InP substrate, the resulting LED wafer exhibits exceptionally low surface roughness (1.1 nm) and well‐defined, sharp interfaces within the heterostructures. Furthermore, this MQW LED exhibits favorable emission properties, including a low turn‐on field, minimal efficiency droop, and stable emission wavelength across varying injection currents. These advancements underscore the potential of such short‐wave infrared emitters for scalable applications in fields such as inspection, optical on‐chip communication, and biomedical diagnostics.