Microampere threshold current operation of GaAs and strained InGaAs quantum well lasers at low temperatures (5 K)

The operation of ultralow threshold current GaAs and InGaAs quantum well lasers at cryogenic temperatures has been studied. In particular the threshold current I_th and lasing wavelength of GaAs and strained InGaAs lasers have been measured as a function of temperature from 300 down to 5 K. I _th can in both lasers be characterized by a linear function of temperature up to 200 K, with a significantly (2.5×) larger dI _th/dT for the GaAs laser. We measured a minimum threshold current of 120 μA for the GaAs laser and 165 μA for the InGaAs laser at 5 K. We derive a simple expression for the transparency carrier density as a function of temperature and effective masses to explain our results.