ZnSe‐based laser diodes: New approaches

Abstract

In this paper we report on recent results concerning conventional edge emitting laser structures containing either quantum wells or quantum dots as region and vertical-cavity surface-emitting lasers. In the first part a series of four similar laser structures containing quantum wells with an emission wavelength of 520 nm was grown by molecular beam epitaxy in order to perform a systematic study of lifetime improvement. They differed in the alternating implementation of an additional 5 nm thick ZnSSe layer with a high sulfur composition of 25 % neighboring the quantum well. A high stability of the CdZnSSe active layer was observed by introducing such a kind of strain compensating layers. Lifetime measurements showed a significant improvement up to one order of magnitude using p-and n-& p-side layers. In the second part electro-optical characteristics of ridge and planar CdSe quantum dot laser diodes were compared. A reduction of the threshold current density by a factor of 4.7 for the ridge structure was obtained. This has to be associated to the reduction of current spreading inside the laser diodes. Furthermore, a significant slower degradation of CdSe quantum dot structures compared to common ZnSe-based QW structures was observed. An operating time over 2700 h in pulsed mode experiments at 50 A/cm 2 in LED mode was achieved. In the third part we report on the realization of an optically pumped monolithic vertical-cavity surface-emitting laser operating at a wavelength of 511 nm. The microresonator has a quality factor of 3200 while the threshold excitation power density for the onset of lasing is 22 kW/cm 2 at room temperature. Micropillars of different diameter fabricated out of this structure show discrete optical modes due to the three dimensional optical confinement of the optical wave.1 Introduction Nowadays for various applications small and compact light sources in kind of semiconductor laser diodes are necessary [1]. They combine the advantages of classical laser, e.g. a coherent light beam at a certain wavelength and the low dimensions which are requirements for new techniques and devices. But many these applications specifically needs light emitters in the green spectra range. Up to now only II-VI-based laser diodes are able to provide such a laser emission. Edge-emitters using CdZnSe or CdZnSSe quantum wells (QWs) as the active part cover the whole wavelength range between 500 nm an 560 nm just by varying the Cd content [2], while a quantum dot (QD) laser diode shows emission at 560 nm [3]. However, the commercialization of ZnSe-based laser diodes is hampered by their limited lifetime [4].A big issue of II-VI LD is the fast degradation caused by the instability of the active region. One problem is the compressive strain of the quantum well due to the Cd content. For an emission in the green-yellow region a Cd content between 20 % and 40 % is necessary. One approach to prevent this kind of degradation is the introduction of additional strain compensating layers. These layers consist out of thin ZnSSe ...

Electrically Driven Quantum Light Sources

“…Electrically pumped QDs formed from three monolayers of InAs capped with a 5 nm strain reducing In 15 Ga 85 As layer provided emission in the NIR. [ 75 ] In this device, a microcavity LED structure was combined with a submicrometre oxide aperture to achieve strong 3D confi nements of both the carrier distribution and the optical fi eld in the QD active region.…”

“…A device containing CdSe QDs operating under electrical excitation was demonstrated and considered suitable for single photons. [ 15 ] Finally, a monolithic resonant cavity LED (RCLED) comprising CdSe QDs showed SPE up to 90 K. [ 101 ] The cavity resonance of the RCLED structure could be used to select the QD emission of the desired wavelength range. The diode structure was grown using MBE on an (001) n-doped GaAs:Si substrate.…”

“…Even if in recent demonstrations the requirement for cryogenic temperature operation has been partially removed [ 11 ] (due to the QD's low exciton binding energy), in the most advanced QD systems, low temperature operation of 4-10 K is still necessary to observe light emission with quantum properties. Other semiconductors (diamond), [ 12 ] nanomaterials in the form of nanowires (NWs), [ 13,14 ] carbon nanotubes, colloidal QDs, [ 15 ] and organic molecules [ 16,17 ] with active quantum systems have all been integrated into p-n or p-i-n junctions with, in some cases, room temperature electroluminescence (EL) with SPE evidence.…”

Mass flux of ZnSe–N–H–Cl chemical vapor transport (CVT) system

“…In solving the flux equations, it is assumed that: (1) equilibrium is always established between the solid and the vapor immediately adjacent to it. (2) The diffusion coefficients of the vapor species are constant within the small temperature range between T s and T g and throughout the ampoule length. For numerical solutions, the Stefan velocity and the diffusion coefficients are needed.…”

“…ZnSe single crystals are promising materials for fabrication of blue light-emitting diodes (LED) [1], laser diodes (LD) [2], mixedcolor LEDs [3], nonlinear opto-electronic devices [4] and so on. The preparation of high-quality ZnSe single crystals is crucial to promote the practical application of this material.…”