Metamorphic materials for indium arsenide transistors

To improve on both the high frequency and low-power aspects of the III-V semiconductor microwave transistor (by definition, the microwave transistor operates at frequencies above 1 GHz), InAs or a related high indium content alloy is incorporated in the base layer of the heterojunction bipolar transistor (HBT) and the channel layer of the high electron mobility transistor (HEMT). These devices must be fabricated on a semi-insulating (SI) substrate for effective microwave performance which becomes a challenge for the high indium content structures due to the large lattice mismatch with the SI substrates that are commercially available (InP and GaAs). A virtual substrate is engineered which has the desired semi-insulating bulk properties and large lattice parameter template for the epitaxial growth of InAs-based microwave devices.; The HBT device, a minority carrier structure, requires a low defect density in the device. This is accomplished with a 0.9 mum compositionally graded InxAl1-xAs (0.52<x<0.86) buffer layer (GBL) grown on a SI InP substrate which results in a threading dislocation density (rhot) of 106 cm-2. Improved thermal properties, process compatibility, and economic feasibility motivate the need for creating a thinner GBL. Quadrupling the grading rate (reducing the thickness to 0.23 mum) of the InxAl1-xAs GBL degrades the materials quality, specifically causing dislocation pile-ups (rho t = 108 cm-2) and an 8-fold increase in surface roughness; the reduced materials quality translates to poor electronic characteristics. The high dislocation velocity of InAs does allow the In xA1-xAs GBL to be grown at double the grading rate (reduced thickness to 0.45 mum) while maintaining equivalent materials and electronic properties.; The HEMT device is constructed using a SI AlSb constant composition buffer layer (CCBL) grown on a GaAs substrate, which has the advantage of a smoother surface morphology and high resistivity.{09}The large amount of strain (8%) introduced at the interface results in a rhot that decreases linearly with buffer thickness. AlSb CCBLs grown to 0.65, 1.27, and 1.72 mum contain 7.7 x 108, 3.1 x 109, and 5.4 x 109 cm-2 threading dislocations, respectively, in the InAs channels of the HEMT devices. The gate leakage current in the device degrades by a factor of 3 from the low to the high rhot samples. No trend is found with room temperature mobility and rhot , however at low temperatures there is a decrease in mobility with high rho t. The dislocation inhibited mobility is modeled analytically and agrees with experimental results.; An alternate approach to creating a narrow bandgap, large lattice parameter virtual substrate is wafer bonding coupled with hydrogen ion implantation and exfoliation. This technique is investigated for metamorphic InAs semiconductors. Key factors taken into consideration are the high diffusivity of hydrogen in the low melting temperature materials and the high density of dislocations in the metamorphic materials. Annealing of the ion implanted metamorphic InAs at 150°C for 10 minutes causes interstitial hydrogen to diffuse away from the implanted region and settle at low energy sites - strained regions around dislocations. Uniform surface blistering is produced at the implantation depth after 5 hours of annealing at 75°C. This effect is explained by the increased diffusivity of hydrogen at higher temperatures.