The key component of a quantum cascade vertical cavity surface emitting laser (QC VCSEL) is a monolithic high-contrast grating (MHCG) that replaces one of the distributed Bragg mirrors (DBR). The grating induces the polarization component necessary to stimulated emission in quantum cascade active regions embedded in MHCG. The complex electrical and optical phenomena defining the performance of the structure depends on the grating parameters (stripes dimensions, position, thickness and doping concentrations). This work presents optimization of QC VCSELs that is aimed to achieve minimal thresholds currents in the pulse operation regime.
This article presents the InAs/GaSb type-II superlattice interband cascade photodetector low-frequency noise analysis. Presented noise measurements were conducted in temperature range 77-300 K and in frequency range 1-10 kHz. The spectral characteristics of the detector noise at various voltages are analyzed. The measured power spectral density is compared to the theoretical prediction. This comparison suggests that noise estimates based on the dark current may not always be valid and the noise source is difficult to be extract. We showed two samples, one of which was characterized by a large leakage currents contribution being directly translated into increased noise.
Measurements of low-frequency noise of type-II superlattice detectors designed for mid-IR wavelengths are used to determine noise limitations, calculate the real detectivity, and study 1/f noise-current correlations in these devices. No 1/f noise connected to the diffusion current is found as opposed to the generation-recombination, shunt, and tunneling currents. The contribution from the shunt current to 1/f noise can be so large that shunt-originated noise dominates in the high-temperature region, in which current is limited by the generation-recombination and diffusion components. It is also demonstrated that devices made of type-II superlattice contain traps generating random processes with thermally activated kinetics, and the activation energies of these traps are determined.
In this paper we present the development of mid-infrared GaAs/AlGaAs QCLs technology and discuss basic
characteristics of lasers fabricated at the Institute of Electron Technology. We also show that reliable simulation methods
which can deal with the complicated physical phenomena involved in the quantum cascade lasers operation are necessary
to predict the behaviour of new structures and optimize their performance. The developed lasers show the record pulse
powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the epitaxial
process and by applying a high reflectivity metallic coating to the back facet of the laser. The devices have been
successfully used in prototype ammonia detection system working in ppb range.
The paper deals with low-frequency noise in RuO2-glass thick resistive films at low temperatures. Careful measurements performed with ac technique reveal that below liquid helium temperature and in the low frequency limit excess noise of the films is a pure resistance noise for low bias voltage, but at larger voltages depends sublinearly on voltage square. The model is proposed which shows that the observed noise suppression is due to inhomogeneous heating of devices under test. In this model conduction is via hopping and the noise is due to fluctuation of activation energies of the inter-site conductances. Numerical simulations show that there is an interesting scaling of noise that can be used to identify the local (microscopic) mechanism of heat transfer from electron to phonon systems.
The process of electronic conduction in granular metals in the dielectric regime is being considered. The charging energy model of conduction in granular metals recently proposed in the literature, is extended to include the effect of the clustering of metallic component which takes place when metal-insulator transition is approached. The electrical conduction is modeled by a resistor lattice built from conductances, Gij equals G0exp(-2chisij-EijlkT), where (chi) is the decay rate of the electron wave function in the insulator, k is Boltzmann's constant and sij and Eij are intergrain separation and intergrain charging energy respectively. The process of clustering of metallic component is introduced as highly conductive bonds which appear in the lattice with average number of B bonds per lattice site. The critical path method is used to find the conductivity, (sigma) , of the model. Temperature dependence of, (sigma) approximately equals exp[-(T1/T)1/2] in agreement with widely observed experiments is found. The temperature, T1, is found to decrease with B increasing i.e. when metal-insulator transition is approached in agreement with experiments reported for real granular metals. Numerical simulations of the model are performed. Quite good agreement between the critical path analysis and numerical data is found.
Numerical simulations of 1/f noise in random networks in which bonds take resistances r approximately equals exp(-(lambda) x), where x is a random variable and (lambda) >> 1, are presented. For microscopic noise generating mechanism which obeys the form of {(delta) r(delta) r} approximately equals r2 $plus (theta ) it is shown that the effective noise intensity C equivalent S(Omega) , where S is the relative power spectral density of the fluctuations (delta) R of the resistance R of the network and (Omega) is the networks volume, is given by C approximately equals (lambda) mexp(- (lambda) (theta) xc) where Xc is related to percolation threshold. Numerical simulations performed for (theta) equals 1 and (theta) equals 0 give m equals 2.3 and show that exponent m is 'double universal' i.e., it is independent of the geometry of the lattice and of microscopic noise generating mechanism.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.