It has generally been recognized that sources of the highest purity facilitate growth of loP and InAlAs with excellent optical and electrical characteristics. The mobility, photoluminescence linewidths, X-ray linewidths, impurity levels, and ultimately device results have been evaluated for two different hydride purity levels. It was found that each of the above characteristics was affected by improved arsine and phosphine purity. The 77 K mobility of lnP increased by a factor of 2 and the InAlAs silicon doping efficiency increased by a factor of 5. Accompanying improvement in device performance, notably the peak to valley ratio of resonant tunneling structures has been observed.

A systematic growth study of InGaAs/AIA5/InGaAsP resonant tunneling hot electron transistors (RHETs) was performed using chemical beam epitaxy (CBE). The resonant tunneling hot electron transistors studied consist of a highly strained AIAs/1n 075Ga525As/AIA5 double barrier structure and an undoped InP collector barrier with 1.1 and 1.2 gm InGaAsP graded layers. These quaternaries were lattice matched to InP within 2.6x iO~and showed an averaged full width at half-maximum (FWHM) of 6 meV from low temperature photoluminescence (PL) measurement. The effects of growth interrupt were studied using PL, X-ray diffraction and secondary ion mass spectrometry (SIMS) measurements, It was found that excessive growth interrupt induced high oxygen accumulation (8x io'~cm 3) at the heterojunction and reduced the intensity of PL spectra. Moreover, for the growth of tunneling heterostructures, low substrate temperature, appropriate growth interrupts and use of hydride drying filters and high purity hydrides were helpful to improve device performance. The highest peak-to-valley current ratio (PVR) observed was 12.7, and maximum base transport ratio was 0.98 at 80 K. Furthermore, some digital functions such as flip-flop gate and exclusive NOR were demonstrated using a single RHET.

The growth of InAIP and related compounds such as InGaP lattice matched to GaAs has attracted a great deal of interest for optoelectronic devices emitting in the range from 638 to 700 nm and for electronic devices such as the heterojunction bipolar transistor. Although some gas source MBE work has been performed in this material system, very little CBE work has been done, largely attributable to the lack of a suitable aluminum source. This is the first report of trimethyl amine alane (TMAA) being used to grow InAIP. TMAA offers advantages of less carbon incorporation and less oxygen sensitivity compared to triethyl aluminum, tri-isobutyl aluminum, or trimethyl aluminum. Trimethyl amine alane has been used to grow AIGaAs HBTs and more recently to grow InAlAs/InGaAs HEMTs by CBE. One of the principal strengths of CBE is its ability to handle phosphorus based compounds efficiently, offering excellent interface control. InAIP films with carbon concentrations below 7x 1017 cm 3 lattice matched ba/al < 2x10-3 with good surface morphology have been grown. Double crystal X-ray diffraction exhibits a single epi-peak with a full width at half max of 46 arc sec with multiple Pendellösung fringes. The epitaxial films are semi-insulating, completely depleted for thicknesses up to 1.6 jsm. Oxygen levels measured by secondary ion mass spectroscopy are comparable to levels measured in InAlAs films (~2.5 x iO'8 cm _3) lattice matched to InP. The likely source of this oxygen is the hydride precursor as has been shown for the growth of InAlAs. As the substrate temperature is raised, the films become increasingly indium-rich. Breaking the growth rate down into its constituent binaries indicates an enhanced TMI incorporation rate. The quality of the films as measured by X-ray full width at half max and the surface morphology is extremely sensitive to substrate temperature. A very narrow window exists for the growth of good quality material in the range from 535 to 545°C.

The InAlAs/InGaAs high electron mobility transistor offers excellent high frequency, low noise operation for amplifiers. While this material system has been grown primarily by conventional MBE, other growth techniques have been examined for improved throughput. The flexibility of chemical beam epitaxy offers semi-infinite sources, good source stability, efficient phosphorus utilization, and extended uptime (more than 560 growth runs over 1.5 years). However, CBE has only recently been shown to produce excellent quality InAlAs suitable for the growth of InAlAs/InGaAs HEMTs [1].This is the first parametric investigation of the properties of InAIAs/InGaAs HEMT5 grown by CBE. A series of lattice matched, pulse doped HEMTs have been grown in which the dopant dose, spacer layer, and channel thickness were systematically varied. Low field 300 K Hall mobilities as high as 8700 cm 2/V s for a sheet carrier concentration of 3 X 1012 cm2 have been measured. This mobility is somewhat lower than uniformly doped HEMTs, which have shown mobilities over 10,000 cm s at room temperature. A figure of merit, the low field conductivity, has been correlated among the device structure, gateless saturation currents, and DC and microwave device performance. Its applicability as a rough predictor of device performance will be discussed. For a given spacer thickness, the mobility improves as the pulse dose is decreased up to a mobility somewhat below that for uniformly doped structures. As the dopant to channel thickness is increased, this saturated mobility also increases. Secondary ion mass spectroscopy has shown no increase in carbon or oxygen levels at the dopant pulse. This has led to speculation that interface scattering at the top InAlAs/InGaAs interface may be important; however, initial SIMS results do not conclusively show intermixing of the Group III elements at this interface. It is possible that a reduction in the substrate temperature during growth may improve any interface roughness. Results of this modification in growth conditions shall be reported. Self-aligned 0.15 /sm HEMTs fabricated from these layers have shown external DC transconductances over 1000 mS/mm, unity current gain cutoff frequencies as high as 190 GHz and unity power gain frequencies above 300 GHz. These results and those of more conventional 0.1~sm gate length HEMTs demonstrate the potential of InAlAs/InGaAs HEMTs grown by CBE.