Temperature and pressure dependence of the recombination processes in 1.5μm InAs∕InP (311)B quantum dot lasers

Abstract

The threshold current and its radiative component in 1.5 m InAs/ InP ͑311͒B quantum dot lasers are measured as a function of the temperature. Despite an almost temperature insensitive radiative current, the threshold current increases steeply with temperature leading to a characteristic temperature T 0 Ϸ 55 K around 290 K. Direct observation of spontaneous emission from the wetting layer shows that some leakage from the dots to the wetting layer occurs in these devices. However, a decrease in the threshold current as a function of pressure is also measured suggesting that Auger recombination dominates the nonradiative current and temperature sensitivity of these devices. It has been suggested that excellent temperature stability, low threshold currents, and high modulation bandwidths can be expected from 1.3 m InAs/ GaAs quantum dot ͑QD͒ lasers, in particular, if the devices are p doped. 1 This has stimulated interest in extending the lasing wavelengths of QD lasers toward 1.55 m for long haul telecommunication applications. In order to reach longer wavelengths the dots have to be larger than that needed for 1.3 m operation. Growing 1.55 m quantum dots on GaAs is therefore difficult because of the large strain that accumulates during the Stranski-Krastanow growth. 2 A possible alternative is to grow InAs dots on InP substrates which have a much smaller lattice mismatch with InAs ͑3.2%͒ compared with GaAs ͑7%͒. Molecular beam epitaxy on ͑100͒ InP substrates has already allowed the growth of quantum dots 3 or quantum dashes, 4 which has led to the demonstration of high performance lasers. 4,5 Also, the use of the specific InP͑311͒B orientation has already allowed three-dimensional confined nanostructures with a QD density as high as 10 11 cm −2 ͑Ref. 6͒ to be demonstrated as well as a low chirp of 2.5 Gb/ s for a directly modulated single mode waveguide laser emitting at 1.6 m. 7 Recently, an InAs/ InP͑311͒B narrow ridge single mode waveguide laser emitting on the ground state at 1516 nm under continuous wave operation at room temperature was reported. 8 In this letter we report on a detailed experimental study of the recombination processes that occur in 1.5 m InAs/ InP ͑311͒B QD lasers. A set of 1.5 mm long, 100 m wide ridge lasers were used for this study. Their active region consists of five layers of dots deposited using the double-cap procedure 9 in a Ga 0.2 In 0.8 As 0.435 P 0.565 waveguide. The dot density is ϳ10 11 dots/ cm 2 , as determined from atomic force microscopy measurements. At room temperature the threshold current densities were typically ϳ500 A / cm 2 and the T 0 ͓=1 / ͑d ln I th / dT͔͒ was ϳ55 K for temperatures ranging from 0 to 50°C. In order to understand the recombination processes which take place in these devices, measurements of the threshold current ͑I th ͒ and its radiative component ͑I rad ͒ were performed as a function of pressure and temperature. The radiative current was determined by integrating unamplified spontaneous emission spectra obtained from a 100 m diameter circular wi...

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