R.E. Leoni

High indium metamorphic HEMT on a GaAs substrate

Metamorphic growth of device structures on GaAs substrates has advanced rapidly in recent years. High quality electronic and optical devices have been demonstrated. Also long-term reliability has been achieved with low noise MHEMT devices. Most of the development emphasis has been with structures conventionally grown on InP substrates. This work is motivated by the lower cost, larger diameter, and greater robustness of GaAs substrates compared to InP substrates. However an important characteristic of metamorphic growth is the degree of freedom in choosing the In/sub x/(GaAl)/sub 1-x/As composition and consequently the lattice constant between GaAs and InAs. Consequently new device structures can be achieved which are not possible by pseudomorphic growth on either GaAs or InP substrates. In this effort, solid source MBE was used to grow metamorphic HEMT structures with high indium content. For the conventional MHEMT, the indium concentration is graded to In/sub 0.52/Al/sub 0.48/As to expand the lattice constant to that of InP. Here the indium content was graded to In/sub 0.64/Al/sub 0.36/As to achieve a larger lattice constant than InP. The resulting surface roughness was examined by AFM. For a 25 /spl mu/m x 25 /spl mu/m area, the RMS roughness was 12/spl Aring/ which is very similar to the roughness present in the conventional MHEMT with less indium content.

Properties of metamorphic materials and device structures on GaAs substrates

In this work, the structural, optical, and electrical properties of metamorphic films are examined and compared to non-metamorphic films. Results for electrical and optical devices are presented. Finally the reliability of metamorphic HEMTs is examined.

Reliability of metamorphic HEMTs on GaAs substrates

Abstract Metamorphic HEMT (MHEMT) technology enables the growth of high indium content channels on GaAs substrates, giving them the performance of InP HEMTs. MHEMT growth techniques use a graded alloy composition buffer layer structure, permitting channel indium contents exceeding 25% without strain. Potential applications include 40 Gb/s fiber optic receivers as well as LNAs for local multipoint distribution systems and satellite communications. Many such applications place stringent requirements on reliability with Belcore standards requiring 106 h median time to failure (MTTF) at 125 °C for power devices. Satellite applications require a LNA projected failure-free service of 15–30 years, implying approximately 107 h MTTF, at 85 °C. Naturally, one will ask “Is MHEMT technology reliable?” From the results of our ongoing work, we show that MHEMT reliability is similar to that of InP HEMTs with ∼106 h MTTF at 125 °C.

A DC-45 GHz metamorphic HEMT traveling wave amplifier

Metamorphic HEMT (MHEMT) technology is capable of providing InP based HEMT performance at GaAs based HEMT levels of manufacturability and cost. This makes the MHEMT an attractive alternative for low noise, high frequency, and wide bandwidth applications. The authors describe the performance of a DC-45 GHz MHEMT traveling wave amplifier (TWA) that is well suited for broadband applications such as 40 Gb/s fiber-optic receivers. The amplifier provides a typical noise figure of 2 dB and output powers in excess of 3 dBm.

Millimeter-wave low noise metamorphic HEMT amplifiers and devices on GaAs substrates

An excellent 0.61 dB minimum noise figure and 11.8 dB associated gain at 26 GHz, have been obtained for a InAlAs/InGaAs metamorphic HEMT on a GaAs substrate. Low-noise amplifiers show under 1.8 dB noise figure with gain greater than 24 dB across 27-32 GHz.

Material properties and performance of metamorphic optoelectronic integrated circuits grown by molecular beam epitaxy on GaAs substrates

Solid source molecular beam epitaxy was used to deposit in a continuous process an integrated metamorphic high electron mobility transistor (HEMT) and PIN photodiode structure. A metamorphic buffer layer was first grown on a GaAs substrate to expand the lattice constant to that of In0.53Ga0.47As used in the device layers. The HEMT layers were subsequently grown followed by the PIN diode structure. Cross-sectional and plan-view transmission electron micrographs showed planar layer interfaces and a dislocation density in the device layers of 1×106 cm−2. The device characteristics of the HEMT transistors were not adversely affected by growth of the PIN structure on top. Also the bandwidth and responsivity of the metamorphic PIN photodiode were comparable to an InP PIN photodiode with similar dark currents. The integrated HEMT/PIN diode circuit had a 3 dB bandwidth 20% greater than a hybrid combination of devices due to a decrease in parasitic losses from device interconnects. The frequency performances of ci...

High-frequency metamorphic p-i-n photodiodes and high-electron mobility transistor transimpedance amplifiers: Candidates for fiber-optic communications

Solid source molecular-beam epitaxy was used to grow metamorphic films on GaAs substrates for optical (1.55 μ) p-i-n photodetectors and transimpedance amplifiers which are key components in a fiber-optic receiver. The p-i-n device structure incorporated an In0.53Ga0.47As photoabsorption layer while the transimpedance amplifier contained a metamorphic high-electron mobility transistor structure with an In0.60Ga0.40As channel layer. All layers were arsenide based which simplified material growth. A 10-μm-diam photodiode exhibited a −3 dB bandwidth of 52 GHz, a responsivity of 0.52 A/W corresponding to an external quantum efficiency of 42%, and a dark current of 7 nA at a 10 V reverse bias. The transimpedance amplifier demonstrated a power gain of 16 dB with a −3 dB bandwidth of 45 GHz. The transistors in the amplifier exhibited a dc reliability of 3×106 h at 125 °C. These performances are very promising for the application of metamorphic devices in the next generation 40 Gbit/s fiber-optic communication system.Solid source molecular-beam epitaxy was used to grow metamorphic films on GaAs substrates for optical (1.55 μ) p-i-n photodetectors and transimpedance amplifiers which are key components in a fiber-optic receiver. The p-i-n device structure incorporated an In0.53Ga0.47As photoabsorption layer while the transimpedance amplifier contained a metamorphic high-electron mobility transistor structure with an In0.60Ga0.40As channel layer. All layers were arsenide based which simplified material growth. A 10-μm-diam photodiode exhibited a −3 dB bandwidth of 52 GHz, a responsivity of 0.52 A/W corresponding to an external quantum efficiency of 42%, and a dark current of 7 nA at a 10 V reverse bias. The transimpedance amplifier demonstrated a power gain of 16 dB with a −3 dB bandwidth of 45 GHz. The transistors in the amplifier exhibited a dc reliability of 3×106 h at 125 °C. These performances are very promising for the application of metamorphic devices in the next generation 40 Gbit/s fiber-optic communication system.

Metamorphic PIN photodiodes for the 40 Gb/s fiber market

High-speed metamorphic PIN diodes that absorb at 1.55 /spl mu/m wavelength light were fabricated on a GaAs substrate. The In/sub 0.53/Ga/sub 0.47/As-based top-illuminated structure showed a low, stable dark current of 7 nA at 10 V reverse bias. The packaged diode demonstrated a -3 dB bandwidth of 52 GHz and 0.52 A/W responsivity. This state-of-the-art diode fabricated on a highly manufacturable GaAs substrate is clearly suitable for the 40 Gbit/s fiber optic telecommunication market, and opens the door for metamorphic OEICs.

Metamorphic optical receiver components

GaAs based metamorphic HEMT (MHEMT) technology has emerged as an attractive, low cost alternative to InP HEMTs. The strain-induced imperfections caused by high indium content layers on GaAs are eliminated in metamorphic devices by providing a properly grown lattice-matching buffer between the substrate and active device layers. Metamorphic device technology has now expanded to optical receiver components and shows performance suitable for 40 Gb/s digital and analog optical links.