Laser Annealing and Dopant Activation in III-V Materials
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For the past 50 years, the electronics industry has profited from their ability to follow Moore’s Law, doubling the performance of the computer chip approximately every two years. Traditionally, these improvements came from reducing the size of the logic switches, or transistors, so that more could fit in a given sized computer chip. However, the electronics industry has hit a roadblock where merely shrinking components no longer improves the performance. To overcome this hurdle, manufacturers are beginning to implement non-traditional device structures and materials into computer chips. Compound semiconductors are strong candidates for materials to replace silicon based on their improved speed and efficiency with, importantly, lower power requirements. III-V materials, like InGaAs and InAs, are promising candidates to replace silicon in areas in the transistor that require high conductivity semiconductors. Low-power device architectures can be realized with GaN and other III-N materials. Although charge-carrying electrons can move much faster in these materials, a fundamental issue is getting enough free electrons into the materials through a process called doping, hence limiting the conductivity that can be achieved. This is the problem that my work addresses-- studying how fast thermal processing could improve the electrical properties of doped III-V and III-N materials. Using sub-millisecond to millisecond laser spike annealing (LSA), we can transiently reach high annealing temperatures, and, in this way, improve conductivity by achieving high active concentrations of dopants in these materials. We have broadly characterized LSA for III-V and III-N materials with a high-throughput, combinatorial processing method. With this method, we explored kinetically limited states that are inaccessible using typical heating approaches like furnace and rapid thermal annealing (RTA). We found that LSA increased the activation of high-dose implanted dopants in InGaAs to a peak concentration beyond a previously established thermodynamic limit, improving dopant activation by a highly significant 29%. In contrast to longer timescale anneals (like those from furnace anneals or RTA), no deactivation is observed during LSA processing for InGaAs samples with dopants grown in to active positions. Our latest LSA studies of implanted GaN resulted in achieving nearly 100% activation of dopants. In these millisecond time frames, LSA is effective for ion-implantation dopant activation and for retention of metastable as-grown dopant concentrations. Our work shows that this kind of metastable processing will be critical to future device applications that use III-V and III-N materials.
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