Anton Yu. Egorov

Negative characteristic temperature of InGaAs quantum dot injection laser

The range of negative characteristic temperatures in temperature dependences of threshold current density of low-threshold (In, Ga)As/(Al, Ga)As quantum dot injection lasers has been observed. A model describing the decrease in threshold current density with temperature at low temperatures is proposed.

Bandedge-engineered quantum well laser

A promising type of quantum well (QW) lasers is discussed—bandedge-engineered (BE) QW lasers. The use of two asymmetric barrier layers (one on each side of the QW) in such lasers prevents establishing a bipolar population in the optical confinement layer (OCL) and thus suppresses the parasitic electron–hole recombination there. We discuss semiconductor alloys suitable for pseudomorphic growth of BE QW lasers on GaAs substrates and propose material compositions for such lasers. We use an analytical model to calculate the device characteristics. Due to suppression of the recombination in the OCL, the threshold current density of a BE QW laser is considerably reduced and the characteristic temperature T0 is increased compared to conventional QW lasers. Ideally, T0 of a BE QW laser can be as high as 300 K at room temperature. In more realistic BE QW lasers incorporating thin indent layers (located between the QW and each of the asymmetric barrier layers), the threshold current density is still low, and T0 is above 200 K for practical cavity lengths. Our results suggest that BE QW lasers offer major advantages over conventional QW lasers for low-threshold and high-temperature-stable operation.

Multi-Stacked InAs/InGaAs/InP Quantum Dot Laser (Jth=11 A/cm2, λ=1.9 µm (77 K))

Self-organized InAs quantum dots inserted in an (In, Ga)As matrix lattice matched to InP substrate were used as an active region of an injection laser. Low threshold (11 A/cm2) lasing at 1.9 nm (77 K) via the quantum dot states was realized. Temperature dependencies of the main laser parameters demonstrate the important role of the nonradiative recombination. An analysis of basic mechanisms of leakage shows that the Auger recombination share is negligible.

1.3-μm edge- and surface-emitting quantum dot lasers grown on GaAs substrates

The development of 1.3 micron VCSELs is currently considered to give a strong impulse for a wide use of ultra-fast local area networks. In the present work we discuss MBE growth and characteristics of InAs/GaAs quantum dot (QD) lasers, we also give characteristics of 1.3 micron QD VCSELs grown on GaAs and compare them with those of 1.3 micron InGaAsN/GaAs QW VCSELs. Overgrowing the InAs quantum dot array with thin InGaAs layer allows us to achieve 1.3 micron emission. Long stripe lasers showed low threshold current density (<100 A/cm2), high differential efficiency (>50%), and low internal loss (1-2 cm-1). Maximum continuous wave (CW) output power for wide stripe lasers was as high as 2.7 W and 110 mW for single mode devices. Uncoated broad area lasers showed no visible degradation of characteristics during 450 hours (60C, ambient environment). 1.3 micron InGaAsN/GaAs QW VCSELs are characterized by higher optical loss and lower differential efficiency than QD VCSELs. Due to high gain in the active region QW VCSELS demonstrate high output power (1 mW). QW VCSELs show extremely low internal round-trip optical loss (<0.05%), low threshold currents (<2 mA), high differential efficiency (40%) and output power (600 microW).

Semiconductor quantum dot lasers

Quantum dot (QD) diode lasers attract currently much attention due to their ability to emit light in the advanced near- infrared region at extraordinarily low threshold current densities. A vertical-cavity surface emitting laser (VCSEL), having a superior beam quality, improved temperature stability, low threshold current, and cost-effective planar fabrication, is also an attractive device variant. Here we discuss the state of the art of these lasers intended for the use in 1.3-μm fiber-optic communications. The discussion is centered on an InAs/GaAs semiconductor QD system. Basic issues of the QD synthesis in the system are addressed. The achievement of the control over the 1.3-μm QD emission is demonstrated. Both, wide-stripe and single-mode edge-emitting lasers are described. The lasers designed have a very low threshold current density, high differential efficiency, and a high output power. Narrow-stripe 1.3-μm QD lasers generate in a single mode, have a record-low threshold current, and produce the continuous-wave (CW) power output in excess of 100 mW. Also, we report on QD VCSELs emitting at 1.3 μm. The design of their cavity and active region are described. The room-temperature CW output power of these lasers is as high as 2 mW. Both, the edge- and surface-emitting lasers satisfy the demands of the fiber optical communication technology.