Diode Active Region Research Articles

Temperature Dependence Model of the Laser Diode Bar Current-Voltage Characteristic

Based on an analysis of differences between the experimentally measured temperature dependence of the current-voltage characteristic (I-V curve) of a laser diode bar (LDB) with AlGaAs/GaAs heterostructure and the dependence obtained in accordance with the well-known model of light-emitting diodes, assumptions were made about the sources of these differences. The agreement between the experimental and modeled dependences is significantly improved by taking into consideration the change in the resistance of LDB layers caused by temperature change. It is shown that when the injection current is known, the measured voltage drop across the LDB can be used to estimate the temperature of the diode active region in order to implement thermal stabilization for solid-state laser pumping systems based on high-power laser diodes.

Microwave-signal generation in a planar Gunn diode with radiation exposure taken into account

Microwave-signal generation in planar Gunn diodes with a two-dimensional electron gas, in which we previously studied steady-state electron transport, is theoretically studied. The applicability of a control electrode similar to a field-effect transistor gate to control the parameters of the output diode microwave signal is considered. The results of physical-topological modeling of semiconductor structures with different diode active-region structures, i.e., without a quantum well, with one and two quantum wells separated by a potential barrier, are compared. The calculated results are compared with our previous experimental data on recording Gunn generation in a Schottky-gate field-effect transistor. It is theoretically and experimentally shown that the power of the signal generated by the planar Gunn diode with a quantum well and a control electrode is sufficient to implement monolithic integrated circuits of different functionalities. It is theoretically and experimentally shown that the use of a control electrode on account of the introduction of corrective feedback allows a significant increase in the radiation resistance of a microwave generator with Schottky-gate field-effect transistors.

A method for determining the ambipolar diffusion length and carrier lifetime in GaAs p-i-n diodes

It was determined that the forward loss resistance as a function of the radius of the active region of typical microwave p-i-n diodes depends on the ratio of the square of the ambipolar-diffusion length to the square of the radius of the diode active region. Based on this regularity, a method was developed that provides simple determination of the ambipolar-diffusion length and the carrier lifetime.

Electroluminescence properties of InGaN/GaN multiple quantum well light emitting diodes

Light emitting diodes (LED) and laser diodes (LD) based on III-Nitrides emitting in visible spectrum have seen an interesting advance these last few years. Here, we present a simulation study of a multi quantum well MQW InGaN/GaN light emitting diode LED, where the diode active region is formed by a series of several periods of InGaN quantum wells (QWs) and GaN quantum barriers (QBs). We will, first, present free carriers distribution within LED active region and device electroluminescence under forward polarisation. We will, secondly, see indium element content of InxGa1-xN wells and number of InGaN/GaN periods impacts on LED optical properties.

Diagnostics of heterostructures of resonant-tunneling diodes during epitaxial growth. I. Estimation of the required accuracy of heterostructure growth

Based on the solution to the one-electron Schrodinger equation, current-voltage characteristics of the resonant-tunneling diode based on GaAs/AlAs are numerically simulated. It is shown that the layer thickness accuracy during epitaxial growth of the diode active region should be no worse than one monolayer.

Hydrodynamic study of terahertz three-dimensional plasma resonances in InGaAs diodes

Using a hydrodynamic model self-consistently coupled to a Poisson solver, we investigate the time and frequency response of InGaAs diodes excited at room temperature by an optical photoexcitation presenting a beating in the terahertz frequency domain. The analysis of the main physical quantities, such as the local electric field and the conduction current density, evidences the presence of strong resonances that are interpreted as three-dimensional plasma oscillations excited by the optical beating. By studying the influence of the geometry and doping of the diode, it is shown that, in most cases, the highly doped contacts mainly control the frequency of the plasma mode while the diode length is a crucial parameter to evidence a second resonance related to the diode active region. Moreover, the amplitude of the plasma resonances can be enhanced at high doping levels and by increasing the level of the optical photoexcitation.

Effect of deep‐level states on current–voltage characteristics and electroluminescence of blue and UV light‐emitting diodes

AbstractCurrent–voltage (I–V) characteristics and electroluminescence spectra of several ultraviolet and blue light‐emitting diodes (LEDs) emitting nominally at 380, 400, 430, and 468 nm were studied. These diodes exhibited an Ohmic regime at low forward biases; then the current increased sharply as bias increased. Several changes in the slope of logarithmic I–V plots indicated that, I ∝ Vx. These changes in the slope were interpreted as single‐carrier space‐charge‐limited (SCL) transport across the diode active region. As bias increased the deep states were filled and for the 400‐ and 468‐nm diodes ideality factors of ∼2 were obtained. This indicated that, as bias increased the transport mechanism changed from SCL conduction to recombination of injected carriers in the space‐charge region. For the 380‐ and 430‐nm diodes, ideality factors >>2 were obtained, although the observed electroluminescence spectrum indicated substantial radiative recombination. For the diode emitting at 430 nm, several peaks including the major peak at ∼424 nm appeared to have resulted from transitions between the conduction‐band edge and deep states, identified from the I–V characteristics, likely to be associated with Zn doping of the InGaN active region. Deep states in the other diodes appeared to be ineffective in the radiative recombination process.

Analysis of interface recombination and self-absorption effect on the performance of QWIP–HBT–LED integrated device

In this paper, the effect of interface recombination and self-absorption within the light emitting diode (LED) active region on the efficiency of QWIP–HBT–LED integrated device is considered. This device is composed of a quantum well infrared photodetector (QWIP), a heterojunction bipolar transistor (HBT) and an LED. The evaluation is based on solving the continuity equation describing the carrier diffusion within the LED active region. Analytical expression describing the effect of self-absorption and surface recombination on the LED quantum efficiency is derived. In addition, the active region width and all interested device parameters are involved. It is observed that the quantum conversion efficiency of the device under consideration is degraded by the self-absorption and interface recombination within the recombined region of the LED. Also, the quantum conversion efficiency of the device is increased with the increase of the LED active region as long as the recombination velocity is above a specified value, while it is decreased with the increase of the LED active region as long as the recombination velocity is below this specified value.

Comparison of GaN and In0.04Ga0.96N p-Layers on the Electrical and Electroluminescence Properties of Green Light Emitting Diodes

We have compared the effects of Mg-doped GaN and In0.04Ga0.96N layers on the electrical and electroluminescence (EL) properties of the green light emitting diodes (LEDs). To investigate the effects of different p-layers on the LED performance, the diode active region structures were kept identical. For LEDs with p-InGaN layers, the p-In0.04Ga0.96N/GaN polarization-related EL peak was dominant at low current levels, while the multiple-quantum-well (MQW) peak became dominant at higher current levels, different from LEDs with p-GaN layers. Also, LEDs with p-InGaN exhibited slightly higher turn on voltages (V on ) and forward voltages (V f ) compared to LEDs with p-GaN layers. However, the MQW related EL intensity was much higher and diode series resistance lower for LEDs with p-InGaN layers compared with LEDs with p-GaN, showing possible improvements in output power for LEDs with p-InGaN layers. The diodes with p-GaN layers typically showed V f of ∼3.1 V at a drive current of 20 mA, with a series resistance of ∼24.7 Ω, while diodes with p-InGaN showed V f of ∼3.2 V, with a series resistance of ∼18.5 Ω, for device dimensions of 230 μm by 230 μm.

Reliability of Long Pulsewidth High Power Laser Diode Arrays

AbstractSpace-borne laser remote sensing systems typically rely on conductively cooled, diodepumped solid-state lasers as their transmitter source. Since space-borne instruments incur high developmental and launch costs and are inaccessible for maintenance, their reliability is of great importance. Therefore, it is crucial to address the reliability of high power laser pump arrays, which essentially dictate the reliability and lifetime of the laser systems. The most common solid-state lasers used for remote sensing applications are Neodymium-based, 1-micron lasers and Thulium/Holmium based 2-micron lasers. 2-micron lasers require a pump wavelength of around 10 to 20 nm shorter compared with 1-micron lasers, and require pump pulse durations 5 to 10 times longer. This work focuses on the long pulsewidth laser diode arrays (LDAs) operating at a central wavelength of 792 nm used for optically pumping 2-micron solid-state laser materials. Such LDAs are required to operate at relatively high pulse energies with pulse durations on the order of one millisecond. However, such relatively long pulse durations cause the laser diode active region to experience high peak temperatures and drastic thermal cycling. This extreme localized heating and thermal cycling of the active regions are considered the primary contributing factors for both gradual and catastrophic degradation of LDAs, thus limiting their reliability and lifetime. One method for mitigating this damage is to incorporate materials that can improve thermo-mechanical properties by increasing the rate of heat dissipation and reducing internal stresses due to differences in thermal expansion and thus increasing lifetime. This paper explains the need for long pulsewidth operation, how this affects reliability and lifetime and presents some results from characterization and life testing of these devices.

Role of energy correlations on Coulomb suppression of shot noise in ballistic conductors contacted to degenerate reservoirs

Coulomb suppression of shot noise in a ballistic diode connected to degenerate ideal contacts is analyzed in terms of the correlations taking place between current fluctuations due to carriers injected with different energies. By using Monte Carlo simulations we show that at low frequencies the origin of Coulomb suppression can be traced back to the negative correlations existing between electrons injected with an energy close to that of the potential barrier present in the diode active region and all other carriers injected with higher energies. Correlations between electrons with energy above the potential barrier with the rest of electrons are found to influence significantly the spectra at high frequency in the cutoff region.

Influence of features of QW InGaAs/(Al)GaAs heterostructures grown by MOCVD on the emission spectrum of single-mode laser diodes

Laser heterostructures with an active layer consisted of two strained InGaAs quantum wells are fabricated by the MOCVD epitaxy method. Single-mode laser diodes with a 3 — 4-μm wide stripe contact are made of the heterostructures and their spectral characteristics are studied. It is found that the spectrum of the diodes consists of two groups of longitudinal modes, which cause the spectral broadening. The power distribution between these groups of modes depends on time, the pump current and the temperature of the active region. It is assumed that such a behavior of the diode spectra is explained by the asymmetry of the composition of the diode active region, which arises due to the segregation of In because of the complicated mechanism of its penetrating in the solid solution during the epitaxial growth. This assumption was confirmed by the study of the active region using a modified Auger spectroscopy method.

1 W CW reliable λ = 730 nm aluminium-freeactive layer diode laser

1 W continuous wave (CW) reliable operation (/spl sim/1000 h) in large transverse spot-size (d/T=0.55 /spl mu/m), compressively strained, InGaAsP (/spl lambda/=0.73 /spl mu/m)-active region diode lasers is demonstrated. The use of tensile-strained InGaP barrier layers provides strain-compensation and results in a weak temperature sensitivity for the threshold current (T/sub 0/=125 K) and external differential quantum efficiency (T/sub 1/=410 K).

InAsSb/InAsSbP light emitting diodes for the detection of CO and CO2 at room temperature

This report describes the epitaxial growth and fabrication of room-temperature InAs0.89Sb0.11/InAs0.48Sb0.22P0.30 semiconductor light emitting diodes operating in the mid-infrared wavelength region near 4.5 µm. The InAs0.89Sb0.11 ternary material used in the light emitting diode active region has a large lattice mismatch with respect to the InAs substrate layer and in order to accommodate this it was necessary to grow a buffer layer with an intermediate composition (InAs0.94Sb0.06). The devices exhibit infrared emission at 4.5 µm and could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 µm and carbon dioxide at 4.2 µm in various applications.

Broadly-tunable resonant-cavity light-emitting diode

Microelectromechanical wavelength tuning is demonstrated for the first time in a resonant-cavity light-emitting diode. The device utilizes a deformable-membrane top mirror suspended by an air gap above a diode-active region and bottom mirror. Applied membrane-substrate bias produces an electrostatic force which reduces the air-gap thickness, and therefore, the resonant wavelength. We report broad tunability of nearly 40 nm and spectral linewidths as narrow as 1.9 nm (2.6 meV) for operation near 950 nm. >

Correlation of low-frequency intensity and frequency fluctuations in GaAlAs lasers

The intensity and frequency noise in single-mode GaAlAs lasers have been measured and the correlation between these instabilities investigated. The measurements were made over the range from 10 Hz to 25 kHz in CSP, TJS, and BH laser structures. It is found that the coherence function for frequency noise and intensity noise from one facet is near unity at the lasing threshold, decreases rapidly with decreasing current below threshold, and also decreases, but more slowly, as the current is increased above threshold. Qualitatively similar behavior is found for the correlation between intensity noise from the two laser facets. Junction voltage fluctuations are not correlated with the other types of noise, except when longitudinal mode hopping is occurring. A model in which both intensity and frequency noise are related to local current variations and optical backscattering in the diode active region is developed to explain the results.

Correlation of Low-Frequency Intensity and Frequency Fluctuations in GaAlAs Lasers

The intensity and frequency noise in single-mode GaAlAs lasers have been measured and the correlation between these instabilities investigated. The measurements were made over the range from 10 Hz to 25 kHz in CSP, TJS, and BH laser structures. It is found that the coherence function for frequency noise and intensity noise from one facet is near unity at the lasing threshold, decreases rapidly with decreasing current below threshold, and also decreases, but more slowly, as the current is increased above threshold. Qualitatively similar behavior is found for the correlation between intensity noise from the two laser facets. Junction voltage fluctuations are not correlated with the other types of noise, except when longitudinal mode hopping is occurring A model in which both intensity and frequency noise are related to local current variations and optical backscattering in the diode active region is developed to explain the results.