Room‐temperature operation of transistor vertical‐cavity surface‐emitting laser

Abstract

We demonstrate the first room-temperature operation of a transistor vertical-cavity surface-emitting laser (T-VCSEL). Fabricated using an epitaxial regrowth process, the T-VCSEL is electrically a Pnp-type bipolar junction transistor and consists of an undoped AlGaAs/GaAs bottom DBR, an InGaAs triple-quantum-well (TQW) active layer, an Si/SiO2 dielectric top DBR, and an intracavity contacting scheme with three electrical terminals. The output power is controlled by the base current in combination with the emitter-collector voltage, showing a voltage-controlled operation mode. A low threshold base-current of 0.8 mA and an output power of 1.8 mW have been obtained at room temperature. Continuous-wave operation was performed up to 50°C .Introduction: Transistor lasers have received significant attention during recent years. Based on the monolithic integration of a heterojunction bipolar transistor (HBT) in a semiconductor laser they provide a number of unique properties as compared to conventional diode lasers [1,2]. A particularly attractive feature is the potential for increased laser modulation bandwidth due to the altered charge dynamics in the base region [3]. Given the growing demand for broadband capacity in optical communication networks this may find important applications. Single-channel data rates of 40 Gbit/s and beyond are e.g. presently considered for local area networks and interconnects. Due to the tough requirements on cost-and powerefficiency, vertical-cavity surface-emitting lasers (VCSELs) are the preferred light-sources for these applications. Whereas VCSELs have been demonstrated with 3dB-bandwidth of 28 GHz [4] and VCSELbased optical links with modulation speeds up to 55 Gbit/s [5], this is approaching fundamental limits. To reach such high and even higher modulation rates over an extended temperature range and with sufficient output power, radically new design concepts are required. Transistor-VCSELs (T-VCSELs) and their potential for high-speed modulation were evaluated numerically by Shi et al. [6], and very recently the first experimental demonstration of a T-VCSEL at low temperature was reported [7], including the voltage controlled operation of such lasers [8].In the present work, we have fabricated and investigated a GaAsbased Pnp-type 980-nm T-VCSEL. Continuous-wave operation is demonstrated up to 50°C with a room-temperature (RT) output power of 1.8 mW for a 10·10-µm 2 device, controlled by the base current in combination with the collector-emitter voltage. To the best of our knowledge, this is the first demonstration of the room-temperature operation of a T-VCSEL.

Performance Optimization of GaAs-Based Vertical-Cavity Surface-Emitting Transistor-Lasers

“…This is compensated by a reduction of the collector region so that all devices have a 6.5- cavity with an emission wavelength of approximately 1000 nm. As compared to our previous design [6,7], the present devices also have a lower Al-content in the AlGaAs emitter region (38 instead of 88%). Hole injection over the forward-biased emitter-base junction (I Eh ); 2) Base current (IB); 3) Part of the emitter hole current that is swept into the collector; 4) Majority-current components due to tunneling of electron-hole pairs at the base-collector junction; and 5) Electron and hole injection over the basecollector junction (only effective in the transistor saturation regime).…”

“…1, has been described in detail elsewhere [6,7]. In short it consists of an undoped 36.5-period AlGaAs/GaAs bottom DBR, a pdoped (Zn: 2·10 17 cm -3 ) GaAs collector region, an n-doped (Si:…”

“…However, these T-VCSELs were only designed for low-temperature operation (-75°C) with an output power below 100 µW [2]. We previously reported lasing from a pnp-type T-VCSEL [6], including mW-range output power and high-temperature operation up to 50°C. However, the light-current-voltage (LIV) characteristics of these devices did not fully match the requirements for a transistor laser.…”

Minority current distribution in InGaAs/GaAs transistor-vertical-cavity surface-emitting laser

“…However, because of the three-dimensional device nature this might be obscured due to local variations in the potential distribution inside the device. This is especially important in transistor vertical-cavity surface emitting lasers (T-VCSELs) [6][7][8] that require special confinement schemes for efficient carrier injection. In our recent study of GaAs-based pnp-type 980-nm T-VCSELs, 8 we demonstrated that it is possible to get efficient lasing even far beyond transistor saturation.…”

“…This is especially important in transistor vertical-cavity surface emitting lasers (T-VCSELs) [6][7][8] that require special confinement schemes for efficient carrier injection. In our recent study of GaAs-based pnp-type 980-nm T-VCSELs, 8 we demonstrated that it is possible to get efficient lasing even far beyond transistor saturation. This was argued to be due to spatial potential variations within the device and the simultaneous occurrences of active and saturation modes at different positions.…”