H. L. Dunlap

Mid-wave infrared diode lasers based on GaInSb/InAs and InAs/AlSb superlattices

We report the characterization of a set of broad‐area semiconductor diode lasers with mid‐wave infrared (3–5 μm) emission wavelengths. The active region of each laser structure is a 5‐ or 6‐period multiple quantum well (MQW) with Ga0.75In0.25As0.22Sb0.78 barriers and type‐II (broken‐gap) Ga0.75In0.25Sb/InAs superlattice wells. The cladding layers of each laser structure are n‐ and p‐type InAs/AlSb (24 A /24 A) superlattices grown lattice‐matched to a GaSb substrate. By tailoring constituent layer thicknesses in the Ga0.75In0.25Sb/InAs superlattice wells, laser emission wavelengths ranging from 3.28 μm (maximum operating temperature=170 K) to 3.90 μm (maximum operating temperature=84 K) are obtained.

Low‐temperature annealing behavior of GaAs implanted with Be

Ion implantation of Be into GaAs, followed by annealing at temperatures above 475 °C, produces layers with strong p‐type conductivity and high hole mobility. Maximum electrical activation of the Be is obtained by 550 °C. Be appears to be the only dopant in GaAs which can be electrically activated at such low temperatures following implantation. At temperatures in the range 500–630 °C, satisfactory electrical results can be obtained by annealing in argon or vacuum without encapsulation. Little change in the electrical properties occurs for subsequent encapsulated annealing at temperatures up to 800 °C for the fluences used.

Electrical properties and atomic distribution studies in ion implanted InP

Abstract The electrical properties and atomic distribution of Be- and Si-implanted InP are presented. Phosphosilicate glass acts as an efficient encapsulant up to anneal temperatures as high as 750°C. Capless annealing was successfully performed in flowing phosphine ambient. The experimental atomic distribution of as-implanted Be and Si are in good agreement with LSS theory. A significant redistribution was observed in 10 14 cm −2 Be-implanted samples on annealing at 650°C. A hole concentration of 6 × 10 13 cm −2 was measured in 750°C annealed, 10 14 cm −2 Be-implantd samples while electron concentrations of 5.2 × 10 13 cm −2 were measured in both 6 × 10 13 , 10 14 cm −2 Si-implanted, 750°C annealed InP samples.

Planar, ion-implanted bipolar devices in GaAs☆

Abstract Selected-area ion implantation using heavy metal masks to define the device geometry has been used to fabricate doubly implanted n  p  n bipolar transistors and planar, isolated p  n junction devices in GaAs. The bipolar transistors exhibited common-emitter current gains as high as 25. Collector-base breakdown voltages of 45 V were observed. The junction diodes (∼200 um dia.) exhibited sub-nanoampere leakage currents at 15 V of reverse bias. Surface leakage appears to be the dominant mechanism responsible for the observed leakage currents. The diode forward current is limited by recomination in the space charge region.

ANNEALING OF IMPLANTED LAYERS IN COMPOUND SEMICONDUCTORS BY LOCALIZED BEAM HEATING TECHNIQUES

A comparative study of the transient annealing of Si- and Se-implanted GaAs has been performed using pulsed and cw lasers and pulsed electron beams. Both low (10 13 cm –2 ) and high (5×10 14 cm –2 ) implant fluences were studied. Activation of low fluence implants was achieved only in electron beam annealed samples co-implanted with Ga and As. Pulsed laser annealing yielded layers with low electron mobilities ( 2 V –1 s –1 ) and apparent dopant activation of 4 to 7%. Much higher mobilities (˜2000 cm 2 V –1 s –1 ) and lower activation were observed in cw laser annealed samples. Pulsed electron beam annealing produced the highest apparent dopant activation (20–35%) and intermediate mobilities (900–1000 cm 2 V –1 s –1 ). Some possible explanations for the differences observed between the various types of annealing are discussed.

Photoemission oscillation measurement of barrier thickness for InAs/AlSb resonant tunneling diodes

AlSb barrier thicknesses ranging from 5 to 12 monolayers have been measured during growth of InAs/AlSb resonant tunneling structures using the photoemission oscillation technique. A plot of peak current density as a function of both measured and estimated barrier thickness confirms that use of the photoemission oscillation technique reduces device performance variations with respect to the conventional time‐based approach to layer thickness control. Our growth scheme involves a significant As background pressure during the AlSb growth which results in incorporation of As in the barrier layer. We have modeled the effect of the As incorporation on device properties and find that our measured peak current values are consistent with these calculations.

CW LASER ANNEALING STUDIES OF DEPOSITED FILMS

CW laser annealing of thin (0.05, 0.1, 0.2, 0.5 μ m) silicon films deposited in UHV on silicon produces high quality epitaxial layers when the annealing is conducted in ultrahigh vacuum (UHV). However, incomplete crystallization occurs when cw laser annealing of these films is carried out in air, and a layer of polycrystalline silicon is formed at the surface. The depth of this disordered region increases monotonically with the thickness of the original deposited layer. Auger analysis of deposited films after air exposure shows the presence of significant amounts of oxygen. We postulate that the rate of solid phase epitaxy (SPE) is reduced sufficiently by oxygen to allow spontaneous nucleation of polycrystallites to compete with SPE and eventually totally inhibit planar epitaxial crystallization of the deposited films.

Laser‐annealed Si and Se Implants for GaAs microwave devices

We have studied the room temperature annealing of Si‐ and Se‐implanted GaAs, using pulsed Nd:YAG (1.06 μm), pulsed KrF excimer (0.25 μm), and scanned cw Ar (0.488, 0.514 μm) lasers as energy sources. Low‐fluence (1013 cm−2) implants similar to those used for microwave FET channel formation and high‐fluence (3–5×1014 cm−2) implants typical of ohmic contact formation applications were annealed. The primary evaluation technique used has been channeling yield topography (CYT), the Rutherford backscattering equivalent of X‐ray mapping in an SEM. Using our apparus, the lowest channeling yield obtainable is about 0.05 of the random equivalent signal level. Yields below 0.1 of random have been obtained with all three laser. The best result to date has been obtained with the KrF laser, which produced a yield of 0.057 of random.

Laser‐annealing behavior of deposited and implant‐produced amorphous Si layers on Si substrates

The use of laser radiation to cause localized heating and thereby induce homoepitaxial crystallization of amorphous Si layers is discussed with regard to two application areas: 1) amorphous‐to‐crystalline conversion of deposited films as a form of epitaxial crystal growth; and 2) recrystallization of Si made amorphous by high‐dose ion‐implantation. The major issues in establishing the utility of laser‐annealing as a substitute for uniform thermal annealing in these two applications is addressed via experimental comparison of thermally annealed specimens with their counterparts subjected to either melt‐inducing or non‐melt‐inducing laser irradiation at different wavelengths. Rutherford backscattering spectra and electrical parameters of alser annealed amorphous silicon are presented. Our results suggest that the growth of polycrystallites may be a limiting process in the general application of cw laser annealing of amorphous films.

DIAGNOSTICS OF LASER-ANNEALED SEMICONDUCTOR MATERIALS USING PHOTOACOUSTIC, RELATED OPTICAL, AND RUTHERFORD BACKSCATTERING TECHNIQUES

Optical absorption of implanted layers in silicon and gallium arsenide has been studied as a means of evaluating the restoration of surface layer crystallinity brought about by laser annealing. Simple transmission measurements using wavelengths near the crystalline absorption edge, as well as photoacoustic techniques have been used to measure the properties of the implanted region over a range of fluence from 10 12 to 10 16 cm –2 . Annealing of the surface layer is manifest by an increase of the transmitted signal level and by a decrease in the photoacoustic output voltage. The measurement is nondestructive, can have the high spatial resolution needed for a detailed examination of the variations of crystallinity across the surface and can be carried out rapidly and conveniently compared to other methods.