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Introduction:

 Diode lasers have always been considered as natural candidates for optoelectronic integration simply because the pi-n structure is basically a pn junction in the III-V semiconductor system and because transistors consist of pn diode combinations. However, all efforts to combine laser diodes with known transistor structures have met with little success [1-4] . Given the tremendous interest lately [5-7] in the application of optical data links to interconnect in the high density data center, the integration of the laser and the transistor becomes the object of great interest since it potentially reduces the size, weight, power and cost of the transceiver. For example, currently the transceiver consists of the laser chip, the detector chip, a laser driver chip and a transimpedance amplifier receiver chip although lately the driver and amplifier chips have been reduced to one chip. By dropping the chip count from 4 or 3 to 1, reductions in power, size and cost may be realized and performance improvements obtained due to the elimination of parasitics. The foremost difficulty is achieving commonality between the structure of the laser and the transistor. The most promising approach is to identify a common layer structure with a common set of metal contacts that may function in the capacity of either the transistor or the laser by a simple rearrangement of how the metal contacts are used to realize different devices. In this situation, the fabrication sequence and the epitaxial sequence become common, thereby eliminating the compatibility problem. A structure is illustrated in Fig.1a, b and c which achieves this duality. The basic building blocks for the structure are the bipolar devices shown in Fig.1a,b which have previously been reported [8] as the BicFET (Bipolar Inversion Channel Field Effect Transistor). These are quantum well HBT’s in which the quantum well performs the function of the base. Figs.1a and b show pδnp and nδpn devices in which the collector currents are flows of holes and electrons respectively and are produced by the injection of electrons and holes into their quantum wells respectively. The collector currents may also be produced by the absorption of light in the quantum wells in which case the BicFET performs as a phototransistor. It is noted that the collector regions for Fig.1a and Fig.1b consist of an intrinsic region terminated in a p contact and an n contact respectively. In actual devices grown by MBE, this intrinsic region would be unavoidably doped p type to a level of 1e16cm-3. The formation of the n collector doped region would then be achieved by ion implant. Therefore the intrinsic (or lightly p doped) region may be shared between the bipolar devices with the p and n quantum wells serving as the collector contacts for the pδnp and nδpn devices respectively. The merged device is shown in Fig.1c where the collector current of the pδnp device flows to the quantum well base of the nδpn device and the collector current of the pδnp device flows to the quantum well base of the nδpn device. Thus the majority carrier in each quantum well is provided by the collector current from the opposing device. This is the structure of a thyristor which is depicted in Fig.1c in its off state. When sufficient collector current is provided by absorption or by electrical injection, the thyristor is switched to its on state as shown by the energy diagram in Fig.1d and laser operation may be obtained. In this condition the internal voltage barrier as denoted by φs in Figs 1c and d between the quantum wells has been substantially reduced so that there is considerable back diffusion of electrons (holes) from the pδnp (nδpn ) quantum wells which supplies minority carriers to the opposite quantum well. There have been other [9,10] reported thyristor-like switching devices with lasing properties, also dedicated to the optical switching application. However, the DOES is unique in its incorporation of two modulation doped interfaces.