Gallium oxide coatings for optoelectronic devices using electron beam evaporation of a high purity single crystal Gd.sub.3 Ga.sub.5 O.sub.12 source.

An optoelectronic lII-V or II-VI semiconductor device comprises a thin film coating with optical characteristics providing low midgap interface state density. A field effect device for inversion channel applications on III-V semiconductors also comprises a thin dielectric film providing required interface characteristics. The thin film is also applicable to passivation of states on exposed surfaces of electronic III-V devices. The thin film comprises a uniform, homogeneous, dense, stoichiometric gallium oxide (Ga.sub.2 O.sub.3) dielectric thin film, fabricated by electron-beam evaporation of a single crystal, high purity Gd.sub.3 Ga.sub.5 O.sub.12 complex compound on semiconductor substrates kept at temperatures ranging from 40.degree. to 370.degree. C. and at background pressures at or above 1.times.10.sup.-10 Torr.

TECHNICAL FIELD 
This invention concerns electronic and optoelectronic devices provided with 
a gallium oxide coating for improved performance. 
BACKGROUND OF THE INVENTION 
Dielectric coatings play an important role in achieving desired performance 
of III--V or II--VI semiconductor optoelectronic devices. Dense, closely 
packed thin films are required to protect the surface, such as light 
emitting or receiving facets, of optoelectronic devices from contamination 
and oxidation. Antireflection coatings (AR) are required on light emitting 
or receiving facets to increase the quantum efficiency of optoelectronic 
devices. Dielectric thin films providing low midgap interface state 
density are required, in particular on light emitting facets, to minimize 
nonradiative energy-dissipating processes such as carrier recombination 
via interface states. Carrier recombination is known to trigger a process 
at laser facets called thermal runaway causing device failure especially 
when operated at high optical power. Inversion channel field effect 
devices require dielectric films providing an unpinned Fermi level and low 
density of interface states below midgap (p-channel device) or above 
midgap (n-channel device) at the dielectric/semiconductor interface. 
Further, hysteresis-free capacitance-voltage characteristics with 
excellent reproducibility of flatband voltage, small flatband voltage 
shift, and small frequency dispersion are required. Also, passivation of 
states on exposed surfaces of electronic III-V devices require low density 
of midgap interface states. 
A variety of materials has been proposed for such layers including 
ZrO.sub.2, Al.sub.2 O.sub.3, SiO.sub.x, SiN.sub.x, SiN.sub.x O.sub.y, 
Y.sub.2 O.sub.3 stabilized ZrO.sub.2, borosilicate glass and gallium 
oxide. The SiO.sub.2 and SiN.sub.x layers are usually deposited by 
sputtering, which can cause damage to the semiconductor surface. 
Electron-beam deposition of coatings such as Al.sub.2 O.sub.3 or ZrO.sub.2 
requires addition of oxygen to get the proper stoichiometry for a desired 
refractive index. This requirement makes it difficult to form the layer 
reproducibly. 
Al.sub.2 O.sub.3, SiO.sub.x, SiN.sub.x, SiN.sub.x O.sub.y, and borosilicate 
glass layers are fabricated with dielectric properties, but exhibit a 
pinned Fermi level near midgap with a midgap state density above 10.sup.13 
cm.sup.-2 eV.sup.-1 when deposited on bare III-V semiconductor layers. The 
midgap interface state density is in a range between 7.times.10.sup.11 
cm.sup.-2 eV.sup.-1 and 10.sup.13 cm.sup.-2 eV.sup.-1 when deposited on 
GaAs samples previously treated by liquid or dry surface passivation 
techniques. The long term stability of liquid passivated 
semiconductor/dielectric interfaces under thermal stress has yet not been 
investigated. Furthermore, large hysteresis (at least a few volts), 
nonreproducible flatband voltage shifts (at least a few volts), large 
frequency dispersion of capacitance, and high interface state densities 
closer to valence or conduction band edge, did not yet allow fabrication 
of inversion channel field effect devices on III-V semiconductor devices. 
On the other hand, gallium oxide thin films deposited in an oxygen radio 
frequency plasma in a vacuum system, in conjunction with a GaAs surface 
previously treated by H.sub.2 and N.sub.2 plasma, gives dielectric/GaAs 
interfaces with midgap density of states well below 10.sup.11 cm.sup.-2 
eV.sup.-1. The realization of inversion channel field effect devices has 
been prevented in this case by large hysteresis (.gtoreq.2 V), 
nonreproducible flatband voltage shift (between 2 and 10 V) and leaky 
gallium oxide films. 
It is therefore an object of the invention to provide a proper coating for 
protection and optical anti-reflection providing low density of midgap 
interface states when deposited on bare III-V semiconductor surfaces, in 
particular on light emitting facets for improved device reliability. It is 
another object of the invention to provide a dielectric thin film in field 
effect devices for inversion channel applications on III-V semiconducting 
substrates. 
SUMMARY OF THE INVENTION 
The invention embodies an optoelectronic III-V or II-VI semiconductor 
device comprising a thin film coating with proper optical characteristics 
providing a low midgap interface state density. The invention further 
embodies a field effect device for inversion channel applications on III-V 
or II-VI semiconductors comprising a thin dielectric film providing 
required interface characteristics. A part of the device structure is also 
applicable to passivation of states on exposed surfaces of electronic 
III-V devices. The thin film comprises a uniform, homogeneous, dense, 
stoichiometric gallium oxide (Ga.sub.2 O.sub.3) dielectric thin film, 
fabricated by electron-beam evaporation of a single crystal, high purity 
Gd.sub.3 Ga.sub.5 O.sub.12 complex compound on substrates kept at a 
temperature within a range of from 40.degree. to 370.degree. C. and at 
background pressures at or above 1.times.10.sup.-10 Torr.

DETAILED DESCRIPTION OF THE INVENTION 
A semiconductor device embodying one aspect of the invention is 
schematically represented in FIG. 1. The device, 10, can be any III-V or 
II-VI laser, light-emitting diode or photodetector. This laser could be a 
GaAs-based distributed feedback (DFB) laser, channeled-substrate buried 
heterostructure (CSBH) laser or a ridge waveguide quantum well laser. Such 
structures are well known in the art and, consequently, are not shown or 
discussed in detail. 
In an exemplary embodiment, device 10 is a ridge waveguide quantum well 
laser. Formed on one mirror facet of semiconductor laser body, 11, is a 
coating, 12, which in this example is an anti-reflection (AR) coating 
having a thickness of about .lambda./4n or odd multiple thereof, where 
.lambda. is the wavelength of emitted light and n is the index of 
refraction of the coating. In the case of a photodetector device, .lambda. 
would be the wavelength of the received light. On the other facet is a 
highly reflective coating (HR), 13, of a suitable material such as 
alternate layers of Si and Ga.sub.2 O.sub.3. As a result of these two 
coatings, the laser is capable of emitting a higher power beam from the 
AR-coated facet than would be the case of an uncoated facet. In a ridge 
waveguide laser, a residual reflectivity of from 1 to 10 percent is 
desirable on the AR coated facet. If the laser is of a DFB type, the AR 
coating will also suppress the normal Fabry-Perot modes of the laser 
cavity so that a single longitudinal mode emission is produced. In systems 
where the laser is optically pumped, both laser facets could be coated 
with the AR layer so that a laser amplifier is produced. Ga.sub.2 O.sub.3 
layer 12 can also act as a coating which does not change the reflectivity 
if the thickness is deposited as an even multiple of .lambda./2n. Such a 
coating is called a passivation coating. In such cases, both facets are 
coated, and the layer serves to prevent degradation of the facets which 
might occur due to operation at high optical powers or the application of 
higher than normal current pulses. 
In accordance with a main feature of the invention, the coating, whether 
used as an AR, HR or passivation layer, comprises stoichiometric Ga.sub.2 
O.sub.3 deposited by electron beam evaporation. High quality, dielectric 
Ga.sub.2 O.sub.3 thin films are deposited by a technique using electron 
beam evaporation of a single crystal high purity Gd.sub.3 Ga.sub.5 
O.sub.12 source. The electron beam deposition is generally conducted in 
accordance with known techniques. See for example U.S. Pat. No. 4,749,255, 
which is incorporated herein by reference. The source material is provided 
within a standard or noble crucible contained in an evacuated evaporation 
chamber. Also included within the evaporation chamber are a source of 
electrons and a holder for supporting at least one semiconductor body 
facets of which are to be coated. The beam of electrons is directed to the 
source material to cause evaporation of the material and deposition on the 
to be coated surfaces. Electron beam evaporation provides no significant 
damages to the semiconductor surface and permits in-situ monitoring of the 
layer thickness. 
In a particular example, a number of ridge waveguide lasers with a 
InGaAs/GaAs structure, which comprise InGaAs active regions emitting light 
at 0.98 .mu.m, were placed into the vacuum chamber of the evaporating 
apparatus. The surfaces of the lasers, other than the mirror facets to be 
coated with Ga.sub.2 O.sub.3, where covered by a mask, such as stainless 
steel or resist. The source for the layer to be evaporated was placed in a 
crucible adjacent to the filament so that an electron beam emitted by the 
filament would impinge on the source. The pressure in the chamber is 
typically at or above 1'10.sup.-10 Torr. 
Electron bombardment of the source material was initiated and continued 
until a layer of a desired thickness was evaporated onto the laser facet 
(or facets). Depending whether the facet coating was to be used as an AR, 
HR or passivating coating, the evaporated thickness is adjusted in 
accordance with the desired purpose. Thickness was monitored by a quartz 
crystal oscillator. 
The facet coatings were deposited at the opposite ends of body 11 by a 
process for depositing gallium oxide film disclosed in the copending U.S. 
application Ser. No. 08/217,296 filed on Mar. 23, 1994 (Hunt, N.E.J. et at 
Case 5-1-24-38), which is incorporated herein by reference. The facet 
coatings were deposited by electron beam evaporation of Ga.sub.2 O.sub.3 
using a single crystal high purity Gd.sub.3 Ga.sub.5 O.sub.12 source. This 
source combines the relatively covalent oxide Ga.sub.2 O.sub.3, which 
volatilizes near 2000K, and the pretransition oxide Gd.sub.2 O.sub.3 which 
has a boiling point (&gt;4000K) well above the forgoing temperature. The more 
complex compound Gd.sub.3 Ga.sub.5 O.sub.12 (melting point.about.2000K) 
decrepitates during heating, slowly releasing high purity Ga.sub.2 
O.sub.3. The background pressure in the evaporation chamber (no bleeding 
in of O.sub.2) was 1-2.times.10.sup.-6 Torr. Background pressures as low 
as 1.times.10.sup.-10 or 1.times.10.sup.-11 are possible. The deposition 
rate, which was maintained at 0.05 nm/s, and the film thickness were 
measured during deposition by a crystal thickness monitor. 
Using this method, the facets of ridge-waveguide In.sub.0.2 Ga.sub.0.8 
As/GaAs quantum well lasers were coated with high quality Ga.sub.2 O.sub.3 
films. The so-deposited laser facet coatings exhibited low interface state 
densities. The deposited Ga.sub.2 O.sub.3 films show an excellent 
homogeneity. This was demonstrated by Auger depth profiling as described 
in the above-identified copending U.S. application. The measurements also 
show, within the limits of Auger spectroscopy, that the films are 
stoichiometric. No impurities could be detected by Auger analysis 
(sensitivity 0.1%) including Gd, which is considered to be the dominant 
impurity in our Ga.sub.2 O.sub.3 films. The Gd content estimated by SIMS 
was of the order of 0.1%. 
Optical and electrical properties of Ga.sub.2 O.sub.3 films were determined 
before these films were used for coating laser facets. For this purpose, 
homogeneous, high quality dielectric Ga.sub.2 O.sub.3 films with 
thicknesses between 4 and 400 nm were deposited a) on Si wafers covered by 
a 90 nm thick TiW layer, b) on n+GaAs substrates, and c) on fused silica 
in order to determine electrical and optical properties of these films. 
Subsequently, laser facets were coated at substrate temperatures T.sub.S 
of below 50.degree. C., such as 40.degree. C. with no excess oxygen, and 
below 150.degree. C., such as 125.degree. C., with an oxygen partial 
pressure of p.sub.ox =2.times.10.sup.-4 Torr in the evaporation chamber. 
The index of refraction was determined by reflection, transmission, and 
ellipsometry measurements. The transmission of Ga.sub.2 O.sub.3 films on 
fused silica samples was measured by a tungsten halogen lamp in 
conjunction with a monochronometer. Reflectivity measurements were made 
using an Anritsu optical spectrum analyzer MS9001B1 and a tungsten halogen 
lamp. The wavelength was scanned between 0.6 and 1.2 .mu.m and the results 
of both transmission and reflection measurements were subsequently fitted 
to a theoretical model for an absorbing dielectric film. 
In a particular example, GaAs based ridge waveguide lasers structures 
emitting at 980 nm were investigated. The exemplary ridge waveguide laser 
comprises an 80 .ANG. thick In.sub.0.2 Ga.sub.0.8 As quantum well active 
region, 0.1 .mu.m thick undoped GaAs optical confinement layers, and 1.2 
.mu.m thick Ga.sub.0.5 In.sub.0.5 P cladding layers. The calculated 
reflectivity, R, of an abrupt transition of two media with refractive 
index n.sub.1 (air) and n.sub.3 (III-V semiconducting material), 
respectively, separated by an anti-reflection coating with refractive 
index n.sub.2 and a thickness of .lambda./4n.sub.2, or odd multiple 
thereof, is given by 
##EQU1## 
According to foregoing equation, anti-reflection coatings (zero 
reflectivity) are provided by a facet coating with n.sub.2 =1.88, 1.80, 
and 1.89 on GaAs, Ga.sub.0.5 In.sub.0.5 P, and In.sub.0.2 Ga.sub.0.8 As, 
respectively, at 980 nm wavelength. 
FIG. 2 is a plot of refractive index vs. substrate temperature during 
deposition for Ga.sub.2 O.sub.3 films deposited at a background pressure 
of 1-2.times.10.sup.-6 Torr with no excess oxygen (Curve 21) and with 
2.times.10.sup.-4 Torr oxygen present (Curve 22) in the evaporation 
chamber. The refractive indices of Ga.sub.2 O.sub.3 films deposited with 
2.times.10.sup.-4 Torr oxygen present in the evaporation chamber are 1.78, 
1.80, 1.87, and 1.87 for substrate temperatures during deposition, 
T.sub.s, of 40.degree., 125.degree., 250.degree., and 370.degree. C., 
respectively. Ga.sub.2 O.sub.3 films deposited at a background pressure of 
1-2.times.10.sup.-6 Torr with no excess oxygen show a refractive index of 
1.91 when deposited at a substrate temperature of 40.degree. C. and the 
refractive index is complex (2.06+i0.1) when deposited at 125.degree. C. 
substrate temperature. Thus, over a wide range of deposition conditions, 
Ga.sub.2 O.sub.3 coatings deposited by said method of fabrication, provide 
required refractive indices. Imaginary part of the reflective index is 
represented by the measurement point, 23, in FIG. 2. 
By way of an example only, the reflectivity of a 1250 .ANG. thick Ga.sub.2 
O.sub.3 layer, deposited on a GaAs substrate maintained during deposition 
at 125.degree. C. with O.sub.2 partial pressure of 2.times.10.sup.-4 Torr 
in the evaporation chamber, was also investigated. FIG. 3 shows the 
corresponding plot of reflectivity vs. wavelength. Since ridge waveguide 
lasers require low reflectivity coatings, the thickness of the Ga.sub.2 
O.sub.3 coating was designed to yield a reflectivity of 0.5% at 980 nm 
wavelength. The minimum reflectivity is 0.05% at 907 nm wavelength with a 
refractive index of 1.80 of the Ga.sub.2 O.sub.3 coating. Minimum 
reflexivities of 0.03% were measured on other samples. 
FIG. 4 shows a plot of high-frequency capacitance vs. bias for 
Au/Ti/Ga.sub.2 O.sub.3 /n-type GaAs (Curve 41) and for Au/Ti/Ga.sub.2 
O.sub.3 /n-type Ga.sub.0.5 In.sub.0.5 P (Curve 42) 
metal/insulator/semiconductor structures measured at 300K. The Ga.sub.2 
O.sub.3 films were deposited on bare substrates at substrate temperatures 
of 350.degree. C. (Curve 41) and 125.degree. C. (Curve 42) and with 
2.times.10.sup.-4 Torr oxygen present in the evaporation chamber. The 
capacitance characteristics measured at a frequency of 1 MHz at 300K, 
reveal an unpinned Fermi level and a midgap interface state density of 
about 10.sup.12 cm.sup.-2 eV.sup.-1 and below 10.sup.11 cm.sup.-2 
eV.sup.-1 at Ga/As/Ga.sub.2 O.sub.3 and Ga.sub.0.5 P/Ga.sub.2 O.sub.3 
semiconductor/dielectric interfaces, respectively. Since the interface 
recombination velocity is directly proportional to the midgap interface 
state density, energy dissipating processes such as recombination via 
interface states are reduced by one to two orders of magnitude compared to 
other coatings deposited on bare samples. 
Further, an indirect measure of interface recombination velocity are 
measurements of photoluminescence intensity. The Ga.sub.2 O.sub.3 coatings 
on bare GaAs and bare Ga.sub.0.5 In.sub.0.5 P substrates deposited at 
substrate temperatures of 350.degree. C. and 125.degree. C., respectively, 
and with 2.times.10.sup.-4 Torr oxygen present in the evaporation chamber, 
lead to an increase in photoluminescence intensity by a factor of 1.4 to 
1.7 compared to identical uncoated samples. Other coatings such as 
Al.sub.2 O.sub.3,SiO.sub.x, SiN.sub.x,ZrO.sub.2 and Y.sub.2 O.sub.3 
stabilized ZrO.sub.2, deposited on bare GaAs samples, do not cause an 
increase in photoluminescence intensity compared to uncoated GaAs samples. 
FIG. 5 shows a plot of the optical output as a function of dc current for a 
ridge-waveguide In.sub.0.2 Ga.sub.0.8 As/GaAs quantum well laser emitting 
at 0.98 .mu.m before (Curve 51) and after (Curve 52) facet coating. The 
ridge of this laser is 5 .mu.m wide and 500 .mu.m long. The facets of the 
laser were coated with Ga.sub.2 O.sub.3 films deposited at substrate 
temperatures of 125.degree. C. with an oxygen partial presure of 
2.times.10.sup.-4 Torr in the evaporation chamber. Prior to film 
deposition, the laser facets were cleaned by ethyl alcohol. The thickness 
of the front facet coating was 125 nm, which gives a measured and 
calculated reflectivity of 0.5% and 0.75%, respectively. A thin protective 
layer, 35 nm thick, (thickness &lt;&lt;.lambda./(4n.sub.2) with a measured 
reflectivity of 29% was deposited on the back facet. The intensity ratio 
(Curve 53) characterizes the relation between the external optical 
intensities at the front facet after and before coating. The differential 
quantum efficiency increases by 51% after facet coating. 
It will be appreciated that although the specific examples above describe 
coating of laser facets, the invention is also useful for coating surfaces 
of the light-emitting devices such as light-emitting diodes and 
photodetectors. Although the device structures were formed in GaAs 
substrates with multi-layer of InP, InGaAs and GaAs, the invention should 
be generally applicable to III-V semiconductor materials, whether binary, 
ternary or quaternary, and could be applied to structures including II-VI 
semiconductors. 
This invention further concerns III-V and II-VI semiconductor electronic 
devices, especially field-effect devices for inversion channel 
applications and passivation of states on exposed surfaces of electronic 
devices. FIG. 6 is a schematic representation of a field effect device, 
60, for inversion channel applications comprising means to apply a control 
voltage or bias to a metal field plate 61 including electrical terminal 62 
and conductor 63. A dielectric thin film 64 comprises a uniform, 
homogeneous, dense, dielectric Ga.sub.2 O.sub.3 layer deposited ex situ or 
in situ by electron-beam evaporation of a single crystal, high purity 
Gd.sub.3 Ga.sub.5 O.sub.12 complex compound. The term in situ (in contrast 
to ex situ) characterizes the deposition of said dielectric Ga.sub.2 
O.sub.3 thin film on a MBE grown semiconducting layer without leaving the 
UHV environment. The method for depositing said dielectric Ga.sub.2 
O.sub.3 thin film is as described above and is as disclosed in the 
copending U.S. application Ser. No. 08/217,296 filed on Mar. 23, 1994 
(Hunt, N.E.J. et al Case 5-1-24-38), which is incorporated herein by 
reference. The III-V semiconductor 65 is of weak n-type or of weak p-type 
for p-inversion channel and n-inversion channel applications, 
respectively. An Ohmic contact 66 completes the circuit. The operation 
principles of such devices are well known from Si-MOSFET technology and 
consequently, are not discussed in detail (see, for example, S. M. Sze, 
"Physics of semiconductor devices", John Wiley & Sons, page 366, New York 
1981). 
In a particular example, the Ga.sub.2 O.sub.3 thin films were ex situ 
deposited on bare n-type GaAs substrates by said the above described 
method of fabrication. The GaAs substrates were maintained during 
deposition at 350.degree. C. with O.sub.2 partial pressure of 
2.times.10.sup.-4 Torr in the evaporation chamber. The device was 
completed by fabricating Au/Ti dots 61 of different diameters (50, 100, 
200, 500 .mu.m) on top of Ga.sub.2 O.sub.3 thin films 64 by evaporation 
through a shadow mask and by providing an Ohmic backside contact 66. 
High-frequency (1 MHz) capacitance voltage measurements revealed an 
unpinned Fermi level, excellent reproducibility of flatband voltage and no 
detectable flatband voltage shift. Hysteresis was very small, typically a 
few tens of millivolts or less. FIG. 7 is a plot of corresponding 
interface state density vs. bandgap energy with substrate doping 
concentration of 1.6.times.10.sup.16 cm.sup.-3 (Curve 71), and 
8.6.times.10.sup.16 cm.sup.31 3 (Curve 72). Interface states D.sub.it were 
not detectable below midgap by high frequency measurements using Terman's 
method 
##EQU2## 
where C.sub.i is the capacitance of the dielectric layer per unit area, q 
is the unit charge, V* and V are the measured and calculated bias points, 
respectively, at the same semiconductor surface potential .psi..sub.S 
=.psi..sub.SO, i.e. at identical high frequency capacitances (T. M. 
Terman, "An investigation of surface states at a silicon/silicon oxide 
interface employing metal-oxide-silicon diodes", Solid-State Elect., vol. 
5, page 285 (1962)). The resolution limit of this method is about 
10.sup.11 cm.sup.-2 eV.sup.-1. The midgap interface state density 
determined from FIG. 7 is below 10.sup.12 cm.sup.-2 eV.sup.-1. 
In another example, the Ga.sub.2 O.sub.3 thin films were ex situ deposited 
on bare n-type Ga.sub.0.5 In.sub.0.5 P substrates by the above described 
method of fabrication. The GaAs substrates were maintained during 
deposition at 125.degree. C. with O.sub.2 partial pressure of 
2.times.10.sup.-4 Torr in the evaporation chamber. Specific resistivity, 
dielectric constant and dc breakdown field of said Ga.sub.2 O.sub.3 thin 
film are 4.times.10.sup.12 .OMEGA.cm, 10.2, and 1.91 MV/cm. Frequency 
dispersion of capacitance was less than 5% below midgap within the 
measurement range between 500 Hz and 1 MHz. Again, high-frequency (1 MHz) 
capacitance voltage measurements revealed an unpinned Fermi level, 
excellent reproducibility of flatband voltage and no detectable flatband 
voltage shift. Hysteresis was very small, typically a few tens of 
millivolts or less. FIG. 8 is a plot of corresponding interface state 
density vs. bandgap energy with substrate doping concentration of 
3.times.10.sup.16 cm.sup.-3 (Curve 81), and 3.times.10.sup.17 cm.sup.-3 
(Curve 82). The midgap interface state density is well below 10.sup.11 
cm.sup.-2 eV.sup.-1 and the interface state density increases toward the 
valence band edge to values typically found at the excellent Si/SiO.sub.2 
interface. 
As demonstrated in both examples, the disclosed field effect device meets 
all requirements such as unpinned Fermi level, very low density of 
interface states below midgap (p-inversion channel), excellent 
reproducibility of flatband voltage, no detectable flatband voltage shift, 
small hysteresis (typically a few tens of millivolts or less), and small 
frequency dispersion of capacitance between 500 Hz and 1 MHz (less than 
5%) for inversion channel applications. 
Further, Ga.sub.2 O.sub.3 thin films deposited by said fabrication method 
are useful for passivation of states on exposed surfaces of any kind of 
electronic III-V devices. The interface recombination velocity is directly 
proportional to the midgap interface state density. Since the demonstrated 
midgap interface state density is below 10.sup.12 cm.sup.-2 eV.sup.-1 and 
well below 10.sup.11 cm.sup.-2 eV.sup.-1 at GaAs/Ga.sub.2 O.sub.3 and 
Ga.sub.0.5 In.sub.0.5 /Ga.sub.2 O.sub.3 interfaces, respectively, the 
device performance and reliability are improved by small interface 
recombination velocities. 
Various additional modifications will become apparent to those skilled in 
the art. All such variations which basically rely on the teachings through 
which the invention has advanced the art are properly considered within 
the scope of the invention.