Dilute nitride resonant-cavity light emitting diode

Resonant cavity LEDs (RCLEDs) are a viable and low-cost alternative light source to lasers for optical communication systems in the 1.3 µm O-band. Most work in this area has been conducted on InP-based material, which is inherently costly, devices often require cooling and the refractive index contrast for constructing mirrors is low. Here, we demonstrate a high-performance GaAs-based RCLED using a dilute nitride GaInNAs active layer emitting in the 1.3 μm wavelength window. While previous 1.3 µm RCLEDs have used metallic mirrors on the back of the device, we exploit the high refractive index contrast of the GaAs/AlAs system to place Distributed Bragg mirrors on both sides of the active layer and achieve superior performance. The external quantum efficiency of the devices is 20% and the full width at half maximum of the emission spectrum is 5.2 nm at room temperature, into a narrow angular cone. The emission power from an 88 μm diameter aperture is 0.5 mW, which, together with the narrow spectral linewidth, makes the device suitable for deployment in a coarse Wavelength Division Multiplexing (WDM) communications system

Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam

Focused ion beam (FIB) has been used as an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate atomically thin materials, especially in the extended area, has not yet been elaboratively characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected bright ring-shaped emission around the milled location has been revealed by time-resolved PL spectroscopy with high spatial resolution. Our finding opens new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale

Characterization of temperature dependent operation of a GaInNAs-based RCEPD designed for 1.3 μm

We report the characteristics of the temperature dependent operation of a GaInNAs-based resonant-cavity-enhanced photodetector (RCEPD), designed to be operated at the dispersion minimum optical communication window of 1.3 μm. A Transfer-Matrix Method (TMM) was used to design the structure of the device. The absorption layer of the photodetector is comprised of nine 7 nm-thick Ga0.733In0.267N0.025As0.975(Sb)/GaN0.035As0.965 quantum wells, and 15 and 10 pairs of GaAs/AlAs distributed Bragg reflectors (DBRs) grown as the bottom and top mirrors, to form the cavity of the device. All electrical and optical measurements were carried out over a temperature range from 10 to 40 °C in order to investigate the characteristic of the device. The quantum efficiency is determined to be in the range of 16% (at 10 °C) and 31% (at 40 °C). An excellent wavelength selectivity is observed which changed from 3.7 nm (at 10 °C) to 5.4 nm (at 40 °C). The dark current of the device is measured as 11  nA at 10 °C and 19  nA at 40 °C without bias. The photocurrent at −0.5 V is measured to be 1.5 mA at 25 °C. The high dark current of the device is attributed to weak confinement of the electrons in GaInNAs QW surrounded by the strain-compensator GaNAs barrier layers. The temperature dependent cavity wavelength was analytically calculated and compared with that of experimental results. The temperature dependent linear shifts of the resonance wavelength (dλ/dT) is calculated as 0.077 nm/°C, which is in good agreement with the experimental result, 0.080 nm/°C. Our results reveal that the characteristics of a RCEPD, such as quantum efficiency, FWHM etc., are quite sensitive to temperature changes due to the temperature dependence of the refractive index of the DBRs

Dilute nitride resonant cavity enhanced photodetector with internal gain for the lambda similar to 1.3 mu m optical communications window

We report on a novel dilute nitride-based resonant cavity enhanced photodetector (RCEPD) operating at 1.286 mu m. The RCEPD was fabricated using 21 pairs top and 24 pairs bottom GaAs/AlGaAs distributed Bragg reflectors for mirrors and 7 nm thick nine GaAS/Ga0.65In0.35N0.02 As-0.98 quantum wells as the absorption region

A study on the voltage-dependent response of a GaInNAs-based pin photodetector with a quasi-cavity

We present a characterisation of a GaInNAs/GaNAs quantum well-based photodetector with a bottom distributed Bragg reflector (quasi-cavity). The detector is designed to be used at the 1.3 itm optical fibre communication window. The quantum efficiency of the photodetector is measured as 24% at 1286 nm under -2 V applied reverse bias. As the reverse bias voltage is increased, a carrier multiplication-related increase and oscillations are observed in the voltage-dependent responsivity curve. The observed carrier multiplication is explained by the high electrical field-induced impact ionisation mechanism in the pin junction region, while the observed voltage-dependent oscillations are explained by the Franz-Keldysh effect (FKE). At the wavelength of 1286 nm, which is close to the absorption wavelength of the active region of the photodetector, FKE-related oscillations (FKOs), start at very low reverse bias values and the responsivity of the photodetector is dominated by FKOs. On the other hand, FKOs quench at higher wavelengths and an impact ionisation-related increase at the voltage-dependent responsivity curve dominates. At lambda = 1310 nm, only impact ionisation mechanisms have an effect over the R (V) curve. The multiplication factor for 1310 nm is calculated as M = 12 at room temperature. The applied electric field and excitation wavelength dependence of the absorption coefficient is calculated and a good match with the experimental results at the applied voltages is achieved

Characterization of temperature dependent operation of a GaInNAs-based RCEPD designed for 1.3 mu m

We report the characteristics of the temperature dependent operation of a GaInNAs-based resonant-cavity-enhanced photodetector (RCEPD), designed to be operated at the dispersion minimum optical communication window of 1.3 mu M. A Transfer-Matrix Method (TMM) was used to design the structure of the device. The absorption layer of the photodetector is comprised of nine 7 nm-thick Ga0.733In0.267N0.025As0.975(Sb)/GaN0.035As0.965 quantum wells, and 15 and 10 pairs of GaAs/AlAs distributed Bragg reflectors (DBRs) grown as the bottom and top mirrors, to form the cavity of the device. All electrical and optical measurements were carried out over a temperature range from 10 to 40 degrees C in order to investigate the characteristic of the device. The quantum efficiency is determined to be in the range of 16% (at 10 degrees C) and 31% (at 40 degrees C). An excellent wavelength selectivity is observed which changed from 3.7 nm (at 10 degrees C) to 5.4 nm (at 40 degrees C). The dark current of the device is measured as 11 nA at 10 degrees C and 19 nA at 40 degrees C without bias. The photocurrent at -0.5 V is measured to be 1.5 mA at 25 degrees C. The high dark current of the device is attributed to weak confinement of the electrons in GaInNAs QW surrounded by the strain-compensator GaNAs barrier layers. The temperature dependent cavity wavelength was analytically calculated and compared with that of experimental results. The temperature dependent linear shifts of the resonance wavelength (d lambda/dT) is calculated as 0.077 nm/degrees C, which is in good agreement with the experimental result, 0.080 nm/degrees C. Our results reveal that the characteristics of a RCEPD, such as quantum efficiency, FWHM etc., are quite sensitive to temperature changes due to the temperature dependence of the refractive index of the DBRs. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved

Dilute nitride resonant cavity enhanced photodetector with internal gain for the λ ∼ 1.3μm optical communications window

We report on a novel dilute nitride-based resonant cavity enhanced photodetector (RCEPD) operating at 1.286μm. The RCEPD was fabricated using 21 pairs top and 24 pairs bottom GaAs/AlGaAs distributed Bragg reflectors for mirrors and 7nm thick nine GaAs/Ga0.65In0.35N0.02 As0.98 quantum wells as the absorption region. For a 15m diameter window, the photocurrent at 1286nm is 27 μA and 42 μA, at V=0 and 1V respectively, whereas the dark current is as low as 1.7nA at 1V. At the operating wavelength, an excellent wavelength selectivity with a full width at half maximum (FWHM) of 5 nm, and a high quantum efficiency of 43% are demonstrated. The device exhibits significant internal gain at very small reverse bias voltages of V ⩾2V with an overall quantum efficiency of 67%. These are the best ever recorded values for a dilute nitride RCEPD

A study of electric transport in n- and p-type modulation-doped GaInNAs/GaAs quantum well structures under a high electric field

We present the results of longitudinal carrier transport under a high electrical field in n- and p-type modulation-doped Ga0.68In0.32NyAs1-y/GaAs (y = 0.009, 0.017) quantum well (QW) structures. Nitrogen composition-dependent drift velocities of electrons are observed to be saturated at 1.7 x 10(7)cm s(-1) and 1.2 x 10(7)cm s(-1) at 77 K for the samples with y = 0.009 and y = 0.017, respectively, while the drift velocities of holes do not saturate but slightly increase at the applied electric field in the range of interest. The hole drift velocity is observed to be higher than the electron drift velocity. The electron mobility exhibits an almost temperature-independent characteristic. On the other hand, the hole mobility exhibits a conventional temperature dependence of modulation-doped QW structures. As the temperature increases, the drift velocity of the electrons exhibits an almost an temperature-insensitive characteristic, but, on the other hand, for holes, drift velocity decreases approximately from 10(7)-10(6)cm s(-1). It is observed that the drift velocities of electrons and holes are N-dependent and suppressed at higher electric fields. Furthermore, experimental results show that there is no evidence of negative differential velocity (NDV) behaviour for both n- and p-type samples. To explore the observed electron and hole drift velocity characteristic at high electric fields, we use a simple theoretical model for carrier transport, which takes into account the effect of non-drifting hot phonons. The mobility mapping technique (comparison method) is used to extract hot hole temperature in order to employ it in the non-drifted phonon distribution and to obtain the drift velocity-electric field curves. Then hot electron temperatures are obtained from the drift velocity-electric field curves as a fit parameter using non-drifted hot phonon dynamics The analytical model is well-matched to the experimental upsilon(d)-E curves, indicating that carrier-hot phonon scattering is the main reason for suppressing the NDV mechanism in GaInNAs/GaAs QW structures with a carrier density higher than 10(17)cm(-3)

Influence of nitrogen on hole effective mass and hole mobility in p-type modulation doped GaInNAs/GaAs quantum well structures

Nitrogen dependence of hole effective mass and hole mobility in p-type modulation doped Ga0.68In0.32NyAs1-y/GaAs quantum well structures with y = 0, 0.009, 0.012, 0.017 are investigated using magnetotransport and Hall effect measurements. Observed N-dependent reduction of the hole effective mass is explained by stronger confinement of holes. Hole effective mass is also found to have hole density dependence due to the strain-induced valance band non-parabolicity. A tendency to decrease in hole effective mass upon annealing can be attributed to the reduction of well width and/or decrease in hole density. A significant improvement in low temperature hole mobility is observed after annealing. (C) 2013 AIP Publishing LLC

Temporal Response of Dilute Nitride Multi-Quantum-Well Vertical Cavity Enhanced Photodetector

The temporal response characteristics of a GaInNAs-based vertical resonant cavity enhanced photodetector device are presented for operation at lambda ae 1.3 mu m. The absorption layers of the device are composed of nine 7-nm-thick Ga0.65In0.35N0.02As0.98 quantum wells and are sandwiched between top and bottom AlGaAs/GaAs distributed Bragg reflectors (DBRs). The temperature dependence of the transient photoconductivity (TPC) under different light intensities and bias voltages is reported. Photoluminescence measurements were also performed on structures with and without the top DBR to determine their optical response under continuous illumination. The response time was measured using excitation from a 1047-nm pulsed neodymium-doped yttrium lithium fluoride laser with pulse width of 500 ps and repetition rate of 1 kHz. The rise time of the TPC was 2.27 ns at T = 50 K, decreasing to 1.79 ns at T = 300 K. The TPC decay time was 25.44 ns at T = 50 K, decreasing to 16.58 ns at T = 300 K. With detectivity of and noise-equivalent power of , the proposed device is faster and more sensitive with better signal-to-noise ratio compared with other GaInNAs-based resonant cavity enhanced photodetectors (RCEPDs) for operation at 1.3 mu m