Internal quantum efficiency (IQE) is studied in a large set of polar and non-polar InGaN/GaN quantum well structures, 57 samples in total. In search for universal factors limiting IQE, the...

Spectrally and spatially‐resolved nonlinear optical techniques were combined with the photoluminescence spectroscopy to study carrier dynamics and photoluminescence efficiency in highly excited blue‐ and green‐emitting InGaN/GaN quantum wells. The differential transmission and transient grating techniques provided carrier lifetimes and diffusivity in the extended states with energies above the photoluminescence emission band and revealed their dependences on excess carrier density. At high excitation conditions, an increase of diffusivity led to the increase of nonradiative recombination rate, being more pronounced in the green QW structures with respect to the blue ones. Enhancement of these processes in the extended states has a strong impact on diminishing the photoluminescence efficiency in the localized states.

Indium nitride has a good potential for infrared optoelectronics, yet it suffers from fast nonradiative recombination, the true origin of which has not been established with certainty. The diffusion length of free carriers at high densities is not well investigated either. Here, we study carrier recombination and diffusion using the light-induced transient grating technique in InN epilayers grown by pulsed MOCVD on c-plane sapphire. We show that direct Auger recombination governs the lifetime of carriers at densities above ~1018 cm−3. The measured Auger recombination coefficient is (8 ± 1) × 10−29 cm−3. At carrier densities above ~5 × 1019 cm−3, we observe the saturation of Auger recombination rate due to phase space filling. The diffusion coefficient of holes scales linearly with carrier density, increasing from 1 cm2/s in low-doped layers at low excitations and up to ~40 cm2/s at highest carrier densities. The resulting carrier diffusion length remains within 100–300 nm range, which is comparable to the light absorption depth. This feature is required for efficient carrier extraction in bipolar devices, thus suggesting MOCVD-grown InN as the material fit for photovoltaic and photonic applications.

We present a comprehensive study of photoexcited carrier dynamics in differently grown InGaN/InGaN multiple quantum well (MQW) structures, modified by insertion of a wide interlayer structure and subsequent growth of differently shaped quantum wells (rectangular, triangular, trapezoidal). This approach of strain management allowed the reduction of dislocation density due to gradually increasing In content in the interlayer and shaping the smooth quantum well/barrier interfaces. A set of c-oriented MQW structures emitting at 470 nm were grown at Vilnius University, Institute of Applied Research, using a closed coupled showerhead type MOCVD reactor. Photoluminescence (PL) spectra of MQW structures were analysed combining continuous wave and pulsed PL measurements. Reactive ion etching of the structures enabled discrimination of PL signals originated in the InGaN interlayer structure, underlying quantum wells, and quantum barriers, thus providing growth-related conditions for enhanced carrier localization in the wells. Time-resolved PL and differential transmission kinetics provided carrier lifetimes and their spectral distribution, being the longest in triangular-shape QWs which exhibited the highest PL intensity. The light-induced transient grating (LITG) technique was used to determine the spatially averaged carrier lifetime in the entire heterostructure, in this way unravelling the electronic quality of the LED internal structure at conditions similar to device performance. LITG decay rates at low and high excitation energy densities revealed increasing with photoexcitation nonradiative recombination rate in the triangular and trapezoidal wells.