Short period InGaAs/AlInAs THz quantum cascade laser in thin double metal cavities operating up to 188K

Abstract

We present a two-well terahertz (THz) quantum cascade laser designed for high temperature operation based on the InGaAs/AlInAs material system. The lighter effective mass and higher energy barriers increase the gain at high temperatures (T > 150K). When processed in copper-based double metal waveguides the devices show laser action up to a maximum operating temperature of 188K with a maximum current density of 1.4kA/cm$^2$. The low Joule heating due to reduced active region thickness and low electrical bias allows operation at 10% duty cycle up to a temperature of 170K.

Figures (3)

• Figure 1: a) Bandstructure of EV2795 in the Wannier-Stark basis. The laser levels as well as the first parasitic level are highlighted. The colorscale shows the carrier concentration as calculated by NEGF. b) Gain and current density in dependence of bias per period of EV2795. Calculations were performed at 300K with e-e scattering enabled. c) Calculated gain spectrum at a bias of 66m V /period.
• Figure 2: a) Light-Current-Voltage characterisation of a wet etched ridge device from epilayer EV3036. The layer sequence is 29.34/102.181/14.721/99.865/30/67.348 with AlInAs barriers in bold and the underlined layer doped with 1.3. The device is 750µ m long and 150µ m wide. Maximum operating temperature is 154K. b) Light-Current-Voltage characterisation of a wet etched, 1.75m m long and 130µ metre wide ridge device from epilayer EV3105 lasing up to 164K. The nominal layer thicknesses are 25.255/102.181/14.721/99.865/30/67.348 with the same doping as EV3036. XRD measurements determined the period length to be -2.3% of the nominal value.
• Figure 3: a) Light-Current-Voltage characterisation of EV3105. The device is 1.2m m long and 150µ m wide. The laser was driven with $\sim$ 70ns long pulses at a repetition rate of 415 and lases up to 188K. Inset: J$_\mathrm{th}$ behaviour with increasing temperature. The best device shows exceptionally high T$_0$=344K. b) Spectral emission for a 750µ m long and 100µ m wide ridge device driven at 20% duty cycle. At lower temperature the laser operates in a broadband regime due to the highly diagonal lasing transition collapsing to a narrowband state around 3.7T Hz at temperatures above 170K.