A. F. Tsatsulnikov

Gain characteristics of quantum dot injection lasers

Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground-to-excited state transition was observed with increasing threshold gain. An empirical equation is proposed to fit the current density dependence of the QD gain. This fitting equation is shown to be valid for both the ground and excited state lasing in the systems under study in the 77-300 K temperature range. The effect of QD surface density on gain characteristics is calculated analytically.

Low-threshold injection lasers based on vertically coupled quantum dots

We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs). VECODs are self-organized during successive deposition of several sheets of (In,Ga)As quantum dots separated by thin GaAs spacers. VECODs are introduced in the active region of a GaAs-A1GaAs GRIN SCH lasers. Increasing the number of periods (N) in the VECOD leads to a remarkable decrease in threshold current density ( ~ 100 A/cm 2 at 300 K for N = 10). Lasing proceeds via the ground state of the quantum dots (QD) up to room temperature. Placing the QD array into an external AIGaAs--GaAs quantum well allows us to extend the range of thermal stability of threshold current density (To = 350 K) up to room temperature. Using (In,Ga)As-(A1,Ga)As VECODs in combination with high temperature growth of emitter and waveguide layers results in further reduction of threshold current density (60-80 A/cm 2, 300 K) and increase in internal quantum efficiency (70%). Room temperature continuous wave operation (light output 160 mW per mirror) and lasing via the states of QDs up to I = (6-7) Ith have been demonstrated.

Gain and threshold characteristics of long wavelength lasers based on InAs/GaAs quantum dots formed by activated alloy phase separation

Experimental and theoretical study was made of injection lasers based on InAs/GaAs quantum dots (QDs) formed by the activated alloy phase separation and emitting at about 1.3 /spl mu/m. Electroluminescence and gain spectra were investigated. The maximum modal gain is measured experimentally using two different techniques. Threshold current densities as low as 22 A cm/sup -2/ per QD sheet were achieved. A step-like switch from ground- to excited-state transition lasing was observed with an increasing cavity loss. The characteristic temperatures for a sample with four cleaved sides and a 2-mm long stripe device at 300 K were 140 and 83 K, respectively. Single lateral-mode continuous-wave (CW) operation with the maximum output power of 210 mW was realized. Threshold characteristics of a laser were simulated taking into account radiative recombination in QDs, the wetting layer, and the optical confinement layer. The dependence of the threshold current density on the cavity length was shown to be extremely sensitive to the QD-array parameters determining the maximum gain for ground- and excited-state transitions and to the waveguide design. Our analysis reveals that nonradiative recombination channels may play an important role in the laser operation.

Control of the emission wavelength of self-organized InGaAs quantum dots: main achievements and present status

Recent achievements in controlling the electronic spectrum of InAs-based quantum dots (QDs) formed by self-organization phenomena during the initial stages of strained layer epitaxy are reviewed. Three different ways to exercise this control are discussed, based on variation of QD size with the amount of QD material deposited, tuning of the electronic levels in QDs by changing the matrix bandgap, and electronic coupling of neighbouring QDs vertically stacked in the growth direction. Possibilities to prevent thermal evaporation of carriers out of QD states and to tune the emission wavelength in the range 0.85-1.3 µm on GaAs substrates and up to 2 µm on InP substrates are demonstrated.

Formation of InAs quantum dots on a silicon (100) surface

At moderate arsenic fluxes and substrate temperatures (470 ) InAs grows on Si (100) surface in the Stranski-Krastanow growth mode with the formation of mesoscopic dislocated clusters on top of a two-dimensional periodically corrugated InAs wetting layer. In contrast, at lower temperatures (250 ) a dense array of self-organized nanoscale InAs quantum dots of uniform size and shape is formed. These quantum dots, when grown on a Si buffer layer and covered with a Si cap, give a luminescence line at about 1.3 m.

MOVPE of device-oriented wide-band-gap III-N heterostructures

The paper reviews metal-organic vapor phase epitaxy (MOVPE) of some key elements of III-N devices: InGaN quantum wells, InGaN/GaN and Al(Ga)N/GaN short-period superlattices, AlGaN/GaN and InAlN/GaN distributed Bragg reflectors. It is demonstrated that interaction of III-N materials with hydrogen is one of the key processes in MOVPE of these materials. Depending on the desired structure, this process may be fruitfully used or should be suppressed by the proper adjustment of reactor conditions.

High external differential efficiency and high optical gain of long-wavelength quantum dot diode laser

Abstract Long-wavelength (1.29 μm ) lasers grown on GaAs and based on several planes of self-organized quantum dots in an external quantum well demonstrate significant improvement of the external differential efficiency (88%) and the characteristic temperature (150 K ) . This is due to suppression of carrier pile-up in the waveguide region in combination with extended range of optical loss in which the ground-state lasing survives.

A monolithic white LED with an active region based on InGaN QWs separated by short-period InGaN/GaN superlattices

A new approach to development of effective monolithic white-light emitters is described based on using a short-period InGaN/GaN superlattice as a barrier layer in the active region of LED structures between InGaN quantum wells emitting in the blue and yellow-green spectral ranges. The optical properties of structures of this kind have been studied, and it is demonstrated that the use of such a superlattice makes it possible to obtain effective emission from the active region.

Photopumped InGaN/GaN/AlGaN Vertical Cavity Surface Emitting Laser Operating at Room Temperature

Room temperature operation in the wavelength range of 401 to 415 nm has been successfully realized in InGaN/GaN/AlGaN vertical cavity surface emitting lasers (VCSELs) under photoexcitation. The VCSELs are grown by metal-organic vapor phase deposition and composed of a 2l vertical cavity including twelvefold stacked multiple InGaN insertions in a GaN matrix grown on top of a quarter-wave strain-compensated Al0.15Ga0.85N/GaN distributed Bragg reflector.

Active region based on graded-gap InGaN/GaN superlattices for high-power 440- to 470-nm light-emitting diodes

The structural and optical properties of light-emitting diode structures with an active region based on ultrathin InGaN quantum wells limited by short-period InGaN/GaN superlattices from both sides have been investigated. The dependences of the external quantum efficiency on the active region design are analyzed. It is shown that the use of InGaN/GaN structures as limiting graded-gap short-period superlattices may significantly increase the quantum efficiency.